Chapter XXVII…

Chapter XXVII

THE MALAYAN ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS (continued)

THE AGE OF LOCAL DISPERSAL

Synopsis of the Chapter.

HAWAII.—(1) _The Hawaiian residual genera, being those not found in either the Fijian or the Tahitian regions._ The genera especially discussed are Osmanthus, Sicyos, Jacquemontia, Cuscuta, Rumex, Dracæna, Naias, Potamogeton; and amongst others mentioned are Perrottetia and Embelia.

(2) The Hawaiian genera found in Tahiti and not in Fiji. Very few, and illustrated by Byronia, Reynoldsia or Trevesia, Phyllostegia, and Pseudomorus, though it is likely that most of these will be subsequently discovered in Fiji.

(3) The Hawaiian genera found in Fiji and not in Tahiti. Illustrated by Eurya, Gouania, Maba, Sideroxylon, Antidesma, Pleiosmilax, Ruppia.

(4) The absentees from Hawaii. Illustrated amongst the orders by the Sterculiaceæ (see text), the Meliaceæ, the Rhizophoreæ, the Melastomaceæ, and the Coniferæ, and amongst the genera by Trichospermum Loranthus, Stylocoryne, Ophiorrhiza, Alstonia, Hoya, Ficus; and a great many others might be cited.

TAHITI.—(1) The Tahitian residual genera. Only six in number—Cratæva, Buettneria, Berrya, Coriaria, Bidens, Lepinia.

(2) The Tahitian genera found in Hawaii and not in Fiji. See above under (2).

(3) The Tahitian genera found in Fiji and not in Hawaii. (a) Those possessing only species confined to the Tahitian region or to East Polynesia, of which Meryta, Ophiorrhiza, Alstonia, and Loranthus are examples.

(b) Those possessing widely-ranging species besides, often, species confined to the Tahitian region, such as Grewia, Nelitris, Melastoma, Randia Geniostoma, Tabernæmontana, Fagræa, Bischoffia, Macaranga, and Ficus. The widely-ranging species is in many genera polymorphous.

(4) The absentees from Tahiti. Amongst the orders are the Meliaceæ, the Rhizophoreæ, and the Coniferæ. Amongst the genera, usually those with “stones” or large seeds an inch in size, such as Canarium, Dracontomelon, Myristica, Sterculia, Veitchia, &c. Numerous other absent genera might be named.

FIJI.—The Fijian genera not found either in Tahiti or Hawaii. These genera compose about half the Fijian flora, being at least 160 in number. Those especially discussed here are the following:—Hibbertia, Cananga, Sterculia, Trichospermum, Micromelum, Canarium, Dracontomelon, Begonia, Geissois, Dolicholobium, Lindenia, Myrmecodia, Hydnophytum, Couthovia, Limnanthemum, Myristica, Elatostema, Ceratophyllum, Gnetum, Veitchia, Rhaphidophora, Lemna, Wolffia, Scirpodendron. The Coniferæ are dealt with in Chapter XXIV.

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Note appended on Marsilea

HAVING completed our discussion of the general dispersal of tropical genera, chiefly Indo-Malayan, over the Pacific islands, we pass on now to consider the more restricted distribution of non-endemic genera over this region. Here as before we take Hawaii, Tahiti, and Fiji as the three centres of distribution; and here also we deal with the flowering plants after excluding the orchids, the sedges, the grasses, the mountain-plants, and all plants introduced either by the aborigines or by white men.

HAWAII.

After excluding the endemic genera as well as those that are confined to the mountains, we find that this group possesses very few genera that do not occur in the Fijian and Tahitian regions, and fewer still that it owns in common with Tahiti to the exclusion of Fiji. On the other hand, we observe that Fiji possesses a great number of genera, mostly Asiatic in origin, that have not reached Hawaii, and in several cases are not known, from the Tahitian region. These contrasts might have been expected, since the Pacific islands have in later ages been mainly stocked from the Asiatic side of the Pacific, the principal route lying through the Fijian region.

As far as the flora of the lower levels (below 4,000 feet) is concerned, Hawaii only possesses a portion of that which Fiji has derived from the Old World, chiefly through Malaya. Although, as will be shown below, there is a noticeable contribution from America, it is very far from counterbalancing the loss which the Hawaiian flora has sustained in comparison with Fiji through the isolated position of the group. The want of variety, however, in the flora of the Hawaiian lower levels, which up to 4,000 or 5,000 feet represent the islands of the less elevated Fijian region, is in a small degree compensated for by the development of new genera and new species and by the great number of individuals. Trees like Metrosideros polymorpha and Aleurites moluccana, that in the southern groups form only one of many contributors to the forests, rise suddenly into prominence in the northern archipelago and form entire forests. Pandanus odoratissimus largely composes extensive forests in the province of Puna in the large island of Hawaii, extending several miles inland and nearly 2,000 feet up the mountain slopes.

The remarkable contrast between the Fijian flora, which is almost entirely tropical, and the Hawaiian flora, which on account of the great elevation of the islands is temperate as well as tropical, is brought into yet greater prominence when we look at it more closely and treat it numerically. The Hawaiian Group, it must be first observed, though possessing the same area as Fiji and presenting a far greater variety of climatic conditions, has only two-thirds the number of genera of flowering plants (see Chapter XXI., Table B). Whilst at least 200 of the Fijian genera of indigenous plants (excluding the orchids and the grasses) are not found in Hawaii, only about 100 of the Hawaiian genera are absent from Fiji, and the two groups possess about 100 genera in common. When we look more closely at the hundred Hawaiian genera not found in Fiji, we find that about sixty represent endemic genera (thirty-seven) and non-endemic mountain-genera (twenty-two), which naturally are not to be found in Fiji, so that there remain but a small number of genera distinguishing the tropical flora of Hawaii from the Fijian flora. When we take from them a few that occur in the Tahitian region, there is left a very small residuum characteristic of Hawaii alone to the exclusion of the Fijian and Tahitian regions of the South Pacific.

THE HAWAIIAN RESIDUAL GENERA.

It is my purpose now to deal in an illustrative fashion with this Hawaiian residual flora which is composed, as above explained, of the non-endemic tropical genera that are not represented in the Fijian and Tahitian regions. Up to the present we have been dealing with the characters that the floras of Fiji, Tahiti, and Hawaii possess in common as far as tropical genera are concerned. We will now proceed to discuss their differences in this respect, and will begin with the residual Hawaiian flora.

After eliminating two or three genera that will probably be found in Fiji, but including one or two others that are best treated under the endemic genera, about twenty-seven present themselves for our purpose. Nearly all of them possess only endemic species, and belong therefore to an age of dispersal that has passed away. These residual genera plainly indicate that although Hawaii largely received its flora during the age of general dispersal of Old World genera over the Pacific, it was at the same time independently stocked with plants from other sources. They include among others—Cocculus (4), Cleome (1), Perrottetia (1), Mezoneuron (1), Lythrum, Sicyos (8), Peucedanum (2), Campylotheca (12), Senecio (2), Lobelia (5), Embelia (1), Chrysophyllum (1), Rauwolfia (1), Nama (1), Osmanthus (1), Jacquemontia (1), Breweria (1), Cuscuta (1), Lycium (1), Sphacele (1), Phytolacca, Rumex (2), Urera (2), Pilea, Dracæna (1), Naias, Potamogeton. Those printed in italics are regarded as derived from America; whilst the figures in brackets indicate the number of endemic species, nearly all of the genera except the five above indicated possessing only peculiar species, and these five (Lythrum, Phytolacca, Pilea, Naias, Potamogeton) are only represented by species found outside the group.

American genera form a more conspicuous element than they do amongst the genera that have been generally dispersed over the Pacific, those exclusively American being fairly represented, making a third of the whole. We find, for instance, in the Hawaiian “Olomea,” Perrottetia sandwicensis, a small tree that represents in the woods of all the islands the Perrottetias of Mexico and the Andes; whilst with some of those genera that, like Sicyos and Urera, are at home in both the Old and New Worlds, we obtain indications of America being the source of the Hawaiian plants. A few genera again, like Lythrum and Phytolacca, are represented in Hawaii by American species.

Plants with drupes, berries, or other fleshy fruits likely to attract frugivorous birds compose about a third of the total number of these residual genera, whilst fruits or seeds, that were in all probability originally brought entangled in a bird’s feathers, are represented by Sicyos. Some of the genera with stone fruits, such as Osmanthus, to which belongs the Hawaiian Olive, present special difficulties on account of the size of the stone, in this case two-thirds of an inch in length. There are also a number of genera with large dry fruits and sometimes large seeds, of which the method of dispersal is not easy to discover. Thus, Mezoneuron, a Leguminous genus with seeds an inch across (2·5 cm.), and Peucedanum, of the Umbelliferæ, with mericarps half to three-quarters of an inch (1·2 to 1·8 cm.) in length, offer serious difficulties to the student of plant-dispersal. In discussing the difficulty connected with Mezoneuron (see Chapter XV.) he will keep in view the possibility that the original species may have been a littoral plant possessing seeds dispersed by the currents, seeds that lost their buoyancy when the plant established itself inland, just as is now taking place with Afzelia bijuga, a Leguminous littoral tree of Fiji (see Chapter XVII.).

He will also find much to puzzle him in the mode of dispersal of the Hawaiian residual genera of the Convolvulaceæ (Breweria, Jacquemontia, and Cuscuta) that possess only endemic species, and he will speculate as to the manner in which seeds that would seem to possess but little attraction for birds and have no capacity for transportation by the currents could ever have reached these islands, and he will ask himself why it is that the agencies of dispersal, whatever they are, have now ceased to be active. He will perhaps see a way out of his difficulties when he perceives that if isolation has led to the development of peculiar species in Hawaii, it has strangely enough in the case of the Myrsinaceous genus Embelia produced the same effect over the whole range of the genus, and that Hawaii has in this respect derived no advantage from being an oceanic group. According to Carl Mez, nearly all the ninety species of this Old World genus are restricted in their areas, whether continental or insular (“Myrsinaceæ,” Das Pflanzenreich, 1902); and indeed we do not seem justified in assuming that the isolating influences in the case of this genus have been more effective in Hawaii in the mid-Pacific, or in Mauritius in the Indian Ocean, than they have been in continental regions like the Deccan and Nyassa Land, in all of which localities endemic species occur.

The remarkable development of the Cucurbitaceous genus Sicyos, in Hawaii alone of all the tropical Pacific groups, will attract his attention, and he will find here another instance of that predominant principle in the distribution of Pacific plants, where in a widely-ranging genus we find one of its species covering most of its area, whilst the other species are more or less localised. He will wonder at the limitation to Hawaii of a genus like Dracæna, that is so well adapted for dispersal over the Pacific by frugivorous birds; and in endeavouring to explain the presence in the Hawaiian forests of the gigantic Rumex, R. giganteus, he will remember that the small group of Tristan da Cunha, equally isolated in the South Atlantic, possesses an endemic species of the same genus. He will discover in the recognised dispersing agencies of wild ducks and other waterfowl an explanation of the occurrence in Hawaii of the aquatic genera Naias and Potamogeton; but he will be puzzled at their restriction to this group alone of the three tropical Pacific archipelagoes here especially discussed.

Amidst these various perplexities he will probably look with relief on the appearance of Phytolacca brachystachys, an endemic species of the American “pokeweeds”; and he will feel grateful to the American botanists like Professor Weed when they tell him that in the United States crows, blackbirds, and other birds successfully disperse these plants, the seeds of which are sometimes able to pass through the alimentary canal undigested.

But by far the most significant lesson that the student of distribution will carry away from his study of the Hawaiian residual genera will be that which he learns from the genera Embelia and Naias. He perceives here that not only with a typical land-genus has specific differentiation occurred to much the same extent in the continental and insular localities of its range, but that even with a typical genus of submerged aquatic plants, where the conditions of existence are as uniform as they are varied in the case of land plants, the process of differentiation has proceeded on the same broad lines in the interior of a continent and in an island in mid-ocean.

The following notes on some of the residual genera refer more particularly to matters connected with distribution and dispersal.

Osmanthus (Oleaceæ).—This genus, according to the Index Kewensis, contains six species localised in their several habitats of North America, Hawaii, Japan (two), Hongkong, and the Himalayas. Its representative in this group is the Hawaiian Olive, the Olea sandwicensis of Gray, a prevailing tree in the lower and middle woods (1,000 to 4,000 feet) of all the islands, which, like other Hawaiian plants, such as those of the genera Eurya and Antidesma, indicates that the group has been sometimes independently stocked from the regions of the northern hemisphere. The drupe of this tree contains a stone two-thirds of an inch (17 mm.) in length, and suitable for dispersal by frugivorous birds; and birds have evidently distributed the tree all over the group. In fact Mr. Perkins in mentioning the favourite food of birds of the Hawaiian genus, Phaeornis, refers to the fruits of this tree as well as of the Opiko (Straussia) and of the Olapa (Cheirodendron). When, however, we come to consider the feasibility of the stones of the genus having been thus originally carried to Hawaii either from Japan or from North America, we meet with the difficulty presented to us by other Hawaiian genera with stone-fruits, such as Elæocarpus, or with berries containing large seeds, such as Sideroxylon.

Sicyos (Cucurbitaceæ).—This genus comprises about thirty-five known species, of which three-fourths are confined to the New World, being mainly South American, whilst the remainder are restricted to Hawaii, with the exception of two species in the Galapagos Group and Norfolk Island, and a widely-ranging species, S. angulatus. The plant just named, the small fruits of which possess hooked spines, adapting them for dispersal in a bird’s plumage, occurs in Africa, Australia, New Zealand, and America, but has only been recorded in the Pacific islands from the Kermadec Group.

North America was probably the home of the original Hawaiian species. Hillebrand describes eight species, of which five are not found in more than one island, whilst one species is spread over most of the islands. The fruits vary much in size, and only in a couple of species do they now possess any fitness for attaching themselves to plumage, some of them being pubescent or even glabrate, so that deterioration in the capacity for dispersal has here taken place. Their size is usually a quarter to half an inch (6-12 mm.); but it is noteworthy that the species with the largest fruit (Sicyos cucumerinus, one to two inches, or 25 to 50 mm.) is the species most widely dispersed over the group. This appears to indicate that there is some other means of inter-island dispersal in this archipelago than by attachment to birds’ plumage. The isolation of the genus in Hawaii from the rest of the world is, however, complete, since all the species are endemic; and when, therefore, we come to ask how Sicyos angulatus, that has been dispersed in the recent era over America, Australia, and New Zealand, is not found in these islands, we are brought face to face with the ever-recurring difficulty, the suspension in later times of the agency of dispersal in the tropical North Pacific.

Jacquemontia (Convolvulaceæ).—This genus, which is chiefly American, is represented in Hawaii by a peculiar species, J. sandwicensis. This species grows occasionally on the sandy beaches associated with Heliotropium anomalum and Tribulus cistoides; but it is most at home on rocky ground and on old lava-flows near the sea-border, making its abode often in the pockets of black sand produced by the disintegration of the lava. Its small seeds sink in sea-water even after prolonged drying; and it can perhaps be supposed that the original seeds were brought from North America in the crevices of a drifting log. According to Ridley, Fernando Noronha possesses a peculiar species also growing near the sea; and it may be that the drifting log has here been the agent also: but in neither case would this explanation account for the endemic character of the species.

Cuscuta (Convolvulaceæ).—It would seem that with the exception of Hawaii, where an endemic species, C. sandwichiana, occurs, no other oceanic group in the globe possesses a peculiar species of the Dodders. With the exception of an endemic species in New Zealand, and an introduced species in Fiji which is found usually near the gardens of the white residents on Viti Levu, the genus takes but little part in the Pacific floras. The Hawaiian species is a characteristic beach-plant growing on Ipomœa pes capræ, Scævola Kœnigii, Tribulus cistoides, and on other plants that find a permanent or a temporary abode on the beaches. We learn from Ridley and Moseley that Cuscuta americana in Fernando Noronha finds its host also in Ipomœa pes capræ. Since the seeds of the Hawaiian plant and of the introduced Fijian species possess no buoyancy, even after drying for years, we cannot look to the agency of the current unless we call the drifting log to our assistance, and in that case the endemic character of the Hawaiian species would present the difficulty already alluded to in the case of Jacquemontia. The seeds of the Hawaiian plant are about one-twelfth of an inch (2 mm.) in diameter, and as far as size is concerned they might have been transported in a bird’s stomach; but, on account of the rapidity with which the seeds of the genus absorb moisture and swell up, it is most unlikely that they would escape injury. This is one of the several difficulties in plant-dispersal which New Zealand and Hawaii share in common. Further remarks on the germination of the Hawaiian species are made in Note 69.

Rumex (Polygonaceæ).—Hawaii possesses two peculiar species of Rumex, a genus not recorded from any other of the Polynesian groups. One of these species, R. giganteus, is a very remarkable plant, growing to a height of thirty or forty feet when supported by trees. It is noteworthy that the small group of Tristan da Cunha in the South Atlantic possesses a species, R. frutescens, confined to those islands (Bot. Chall. Exped., ii. 154). Both Hawaii and Tristan da Cunha lie in mid-ocean, cut off from the nearest continent by some 1,800 or 2,000 miles of sea; and we may have to choose between the bird and the current in selecting the agency concerned with the transportation of the original seeds; or perhaps they have co-operated. Birds could disperse the nutlets of Rumex as readily as they do those of Polygonum, and I have found these fruits at times in the stomachs of partridges. On the other hand, Rumex fruits occur amongst the drift stranded on beaches in England and in Scandinavia; and, as indicated by the observations of Sernander and myself in these two localities, they float through the winter in ponds and rivers, germinating afloat in the spring. The nutlets sink, but they owe their buoyancy to the persistent perianth. In my sea-water experiments the fruits of Rumex hydrolapathum and R. conglomeratum were still afloat after from six to twelve months’ immersion, and their seeds subsequently germinated. It is quite possible, therefore, that currents can carry these fruits unharmed to oceanic island-groups like Hawaii and Tristan da Cunha.

Dracæna (Liliaceæ).—This Old World genus, which on account of its berries is eminently suited for dispersal by frugivorous birds, is represented in Polynesia by a solitary species (D. aurea) peculiar to the Hawaiian Group. Attaining a height of twenty to twenty-five feet, it often forms a striking feature in the vegetation of the open wooded regions up to altitudes of 3,000 feet. I found it growing in abundance in the large island of Hawaii between Waimanu and Waipio, and on the northern slopes of Hualalai. It grows in a variety of stations, and I came upon it once in the broken-down caverns of an old lava-flow that were frequented by pigeons which no doubt brought the seeds. Its conspicuous yellow berries have hard rounded seeds a quarter of an inch (6 mm.) across and weighing two to three grains when dry, which would probably withstand injury in a bird’s stomach, the minute embryo being protected by a very tough albumen. Neither the entire berry nor the seed could be transported by currents, the last sinking even after drying for six years.

Naias (Naiadaceæ).—If we except New Caledonia, where two or three species have been found, Hawaii is the only island-group in the tropical Pacific from which this interesting world-ranging genus of submerged aquatic plants has been recorded. Chamisso, the celebrated naturalist of Kotzebue’s expedition, collected Naias marina in Oahu in the early part of last century; but apparently it did not come under Hillebrand’s observation in the group. However, in 1897 I found it in another locality, namely, just within the mouth of the Waipio, a river on the north-west side of the island of Hawaii. The mature fruits of this genus have never been experimented on by me; but there is nothing in the structure of the fruits to indicate that they have any buoyancy, or to show that they differ in this respect from the fruits of other completely submerged aquatic plants like Ceratophyllum, Ruppia, and some of the Potamogetons. It is to ducks and other waterfowl that we must attribute the dispersal of this and the other genera just mentioned over wide tracts of ocean, a subject dealt with in discussing those plants.

The Hawaiian Group probably represents the most isolated locality occupied by this genus, since none of the other islands from which species have been recorded, such as New Caledonia, Mauritius, and Bourbon, are so far removed from continental regions. The source of the Hawaiian form of Naias marina lies evidently on the Asiatic side of the Pacific, since it is referred by Mr. Rendle to the variety “angustifolia,” an Asiatic plant found also in the island of Bourbon and in West Australia, but not recorded from the New World. The important little monograph of the genus by Mr. Rendle (“Naiadaceæ,” in Engler’s Das Pflanzenreich, 1901) is full of suggestiveness for the student of plant-distribution. His interest is excited when he discovers that one of the most typical genera of aquatic plants displays the same principle of differentiation at work that is so well illustrated by many of the land genera of the Pacific islands. I refer to the principle implied in the existence of a widely-ranging genus comprising “a polymorphic species occurring over almost the whole area of the genus,” as well as a number of less widely distributed species, most of which have “restricted areas and fall for the most part into small geographical groups.” I have just been quoting Mr. Rendle’s description of the distribution of Naias, the “polymorphic” species concerned being N. marina; but it need scarcely be remarked that it would apply just as well to several of the land genera dealt with in the previous chapter (XXVI.), such as Alphitonia, Metrosideros, Pisonia, &c.

Although there is such a contrast in the degree of uniformity of their life-conditions between land and water plants, a strictly aquatic plant being but slightly affected by changes in the physical conditions that are accompanied by a complete transformation in the character of the terrestrial vegetation, yet—and this is the important point—we find the same principle of differentiation at work with both land and water plants. If one wished to produce proof of the contention that the production of new species is largely independent of external conditions, one could not do better than take the cases of Elæocarpus, Metrosideros, and Naias. In all cases we see a widely-ranging polymorphous species settling down and “differentiating” in particular localities or regions, and forming subcentres for the distribution of the genus.

Potamogeton (Potameæ).—Though well suited for dispersal by waterfowl, the Potamogetons have been recorded from the Hawaiian and Marianne Islands alone among the tropical groups of the open Pacific. The genus, though not so well represented in insular floras as we might have expected, is still not infrequently to be found. Widely-ranging species have been observed in the Azores, Madeira, and the Canaries in the Atlantic, as well as in Hawaii in the Pacific; whilst species have been recorded that are peculiar to Martinique, the Mascarene Islands, and to the Marianne Group. Hillebrand gives for Hawaii, Potamogeton fluitans, a plant of the Old and New Worlds, and P. pauciflorus, a North American species; whilst in the Index Kewensis a peculiar species, P. owaihiensis of Chamisso (which is, however, regarded by Hillebrand as a form of P. fluitans), is also accredited to the group. Owing, however, to the paucity of streams and rivers this genus takes no prominent part in the Hawaiian flora, and the species seem to have been recorded alone from Oahu. As they were discovered by Chamisso in the early part of last century they are in all probability truly indigenous in Hawaii, even if none are peculiar to the group.

That ducks and similar birds are the agents in carrying the seeds of Potamogeton to oceanic islands cannot be doubted. About twelve years ago I examined the stomachs and intestines of thirteen wild ducks obtained in the London market. Three of them contained in all forty-one Potamogeton seeds, or rather “stones,” most of which subsequently germinated in water. In one of my experiments, carried out in the month of December, I fed a domestic duck with the fruits of Potamogeton natans. They appeared in quantity in the droppings, for the most part divested of their soft coverings, but otherwise uninjured. Sixty per cent. germinated in the following spring; whilst of those left in the vessel, from which the duck had been fed, only one per cent. germinated in the next spring, and another year elapsed before any number did so. These results were published in Science Gossip for September, 1894.

One often reads in books of travel interesting remarks bearing indirectly on the dispersal of the Potamogetons. Thus, when Sir Joseph Hooker (then Dr. Hooker) noted in his Himalayan Journals the occurrence of P. natans in the Neongong Lake in the Himalayas, and the presence of coots, he most probably mentioned the bird that brought the plants, coots being active distributors of the seeds of water plants. It is of importance to remember that (as shown in my experiment on the duck) seeds of water-plants are voided in a condition peculiarly favourable to early germination. Ducks, coots, and other water birds might often be characterised as “travelling germinators.” My experiment showed that seven to eight hours at least were occupied by Potamogeton nutlets in passing through the digestive canal of a duck, and that probably nine or ten hours would be required after an average full meal. But this does not represent the possible maximum period, since the bared “stone” may remain in the gizzard for a long time with ordinary gravel. Most of the Potamogeton fruits found by me in wild ducks were obtained from the gizzard, where they were mixed with gravel and other hard seeds or seedvessels, as described in Chapter XXXIII. Such fruits afterwards germinated. With regard to the chances, therefore, of the fruits of Potamogeton being carried by a bird without injury across an ocean, we may infer that, whether they are retained in its body for only ten hours or for as long as three or four days, they will preserve in some cases their germinating power.

HAWAIIAN GENERA FOUND IN TAHITI TO THE EXCLUSION OF FIJI.

Taking only the genera that are strictly indigenous, and excluding therefore all those introduced by the aborigines, the number available for establishing an independent connection between the Hawaiian and Tahitian regions is exceedingly few. Amongst the Hawaiian shore-plants not found in Fiji proper but occurring in the Tahitian region are Heliotropium anomalum and Sesuvium portulacastrum. The last-named, however, has been recorded from Tonga, which lies within the Fijian area; whilst the first will probably be found in the same region. Amongst the Hawaiian and Tahitian mountain genera not recorded from Fiji proper are Nertera, Vaccinium, Cyathodes, and Luzula. As is pointed out in Chapter XXIII., the absence of these genera from Fiji is connected with the relatively low elevation of those islands, though it is quite possible that one or more of them may yet be found on the highest summits of Fiji; and indeed Nertera depressa and Vaccinium have been discovered in the more elevated uplands of Savaii in Samoa.

After removing the littoral plants and the mountain genera, there are probably not more than half a dozen inland genera that connect the Hawaiian lowlands with the Tahitian region to the exclusion of the Fijian Group; and Byronia (Ilicineæ), Reynoldsia or Trevesia (Araliaceæ), Phyllostegia (Labiatæ), and Pseudomorus (Urticaceæ) may be taken as examples. Of these, Pseudomorus, which has a small drupaceous fruit suitable for dispersal by frugivorous birds, has been recorded from New Caledonia, and not improbably it exists in the Fijian area; and the same may be postulated of Reynoldsia, which is discussed in a later page, since it has been found in Samoa. We may almost form the same opinion of Byronia, since it exists in Australia. This genus of small trees contains only three known species, one in Australia, one in Tahiti, and one in Hawaii. Its fleshy drupes, about a third of an inch (8 mm.) in size, would attract birds, and their numerous cartilaginous pyrenes would probably pass unharmed through a bird’s alimentary canal. Phyllostegia, a Labiate genus with fleshy nucules that might attract birds, is, with the exception of a solitary Tahitian species, entirely confined to Hawaii (see Chapter XXII.).

From these data it may be inferred that the interchange of plants between the regions of Hawaii and Tahiti to the exclusion of Fiji has been very slight. The facts of distribution are just such as we might look for in the case of a general dispersal over the oceanic groups of the tropical Pacific, with the altitudes of the islands playing a determining part. In this general dispersal Hawaii has shared; and except in the case of Phyllostegia it is evident that this group has kept nearly all it received and has distributed but little.

HAWAIIAN GENERA FOUND IN FIJI TO THE EXCLUSION OF TAHITI.

We shall be able to throw further light on the floral history of Hawaii by discussing the few tropical genera, not a score in all, that it possesses in common with Fiji to the exclusion of the Tahitian region. The following genera offer themselves for treatment:—Eurya (Ternstrœmiaceæ), Gouania (Rhamnaceæ), Maba (Ebenaceæ), Sideroxylon (Sapotaceæ), Antidesma (Euphorbiaceæ), Pleiosmilax (Smilaceæ), and Ruppia (Potameæ).

These seven genera, which with the exception of Ruppia, an aquatic genus, are only represented in Hawaii by peculiar species, possess in all cases, except Gouania and the last-named genus, drupaceous or baccate fruits likely to attract frugivorous birds. Two of them, Eurya and Antidesma, have their home in Malaya and in the Asiatic continent; three of them, Gouania, Maba, and Sideroxylon, are found on both the Asiatic and the American sides of the Pacific Ocean; whilst Pleiosmilax should, strictly speaking, be regarded as a Polynesian subgenus of Smilax, a world-ranging genus; and Ruppia is a cosmopolitan brackish- and salt-water genus.

It is highly probable that Fiji received almost all these genera from the Old World through Malaya; and in some cases the resemblance between the Malayan and the Fijian species is so close that, as in Gouania, Dr. Seemann questioned if they were not forms of the same species. In other instances, as with Maba, we find a widely-ranging Asiatic and Malayan species, like Maba buxifolia, extending into Western Polynesia, where it is accompanied by other species peculiar to that region. But if the genera were able subsequently to extend their range thence to Hawaii, it is difficult to understand why they have not reached the Tahitian region. It is therefore likely that Hawaii received most of these genera by a northern route and not through the South Pacific; and it is legitimate to suppose that when Old World genera like Eurya and Antidesma occur in north-eastern Asia, as in Japan and in the neighbouring mainland, Hawaii received the genus by that route. In the case of Eurya it is noteworthy that Fijian and Samoan forms, regarded by Seemann and Gray as distinct species, are viewed by Reinecke as forms of E. japonica, an extremely variable species found in Japan. With genera like Gouania and Maba, that exist on both sides of the Pacific, it is possible that they may have originally reached Hawaii from America.

A noticeable feature in the instance of genera like Maba and Sideroxylon is that hard seeds or pyrenes 3/4 to 1 inch (18 to 25 mm.) in length have seemingly been transported by frugivorous birds across the ocean to Hawaii. This at first sight seems improbable; but it is known that fruit-pigeons can swallow very large drupes, as in the case of those of Canarium, Dracontomelon, and Elæocarpus, afterwards disgorging the “stones.” They have carried such stones to Fiji, across some 500 or 600 miles of ocean; and unless we impute a continental origin to Hawaii we must assume that in some cases, as with Elæocarpus, Maba, and Sideroxylon, they have been able to transport these large stones or pyrenes to that group. The extent of ocean to be crossed is no doubt much greater, but this area of the Pacific is not without some small half-way groups that would serve as resting-places.

That fruits of the order Sapotaceæ are much appreciated by fruit-pigeons is already known. We learn from Kirk that the fruits of Sideroxylon costatum (Sapota costata) are a favourite food of the New Zealand fruit-pigeon, the fruits, about an inch long, containing three hard crescentic bony seeds nearly as long as the fruit. The natives of Vanua Levu informed me that a Fijian species of Sideroxylon with hard seeds about an inch long was much appreciated on account of its fruit by the pigeons. I found the hard, sound seeds of a species of Sapota, two-thirds of an inch (or 16 mm.) in size, in the crop of a Fijian fruit-pigeon. The similarly large seeds of a species of Achras were identified by Mr. Charles Moore, of Sydney, amongst a collection of seeds, &c., found by me in the crops of fruit-pigeons shot in the Solomon Islands (Guppy’s Solomon Islands, p. 293). It may be added that the difficulty concerned with Sideroxylon in Hawaii is the difficulty concerned with other large-seeded Sapotaceous trees in Fiji and New Zealand, and the same explanation must be applied to all. Some further remarks on the Sapotaceæ in the Pacific are given below.

The mode of dispersal of some of these genera is illustrated in other regions. The berries of Pleiosmilax, a subgenus of Smilax, are well suited for aiding the dispersal of the genus by frugivorous birds; and we learn from Prof. Barrows (Weed, p. 42) that in the United States crows feed on the fruits of Smilax rotundifolia and disperse the seeds. On the other hand, it is not at first sight easy to understand how a genus like Gouania has been distributed over the tropics of the globe, since it possesses dry capsular fruits about half an inch across, separating into three woody cocci that appear most unlikely to attract birds. The same difficulty exists, however, with other dry-fruited widely-ranging genera like Alphitonia and with many of the Euphorbiaceæ.

Amongst these genera found in Hawaii and Fiji to the exclusion of Tahiti we can at times detect indications of the operations of a polymorphous species as described in Chapter XXVI., when a widely-ranging highly variable species is associated in some groups with peculiar species. We see some evidence of this in the genera Gouania, Maba, and Eurya, alluded to on a previous page. (See also Bot. Chall. Exped., iii. 134, under “Gouania.”)

One of the mysteries of the Pacific is concerned with the distribution of the Sapotaceæ, the dispersal of which by frugivorous birds has been dealt with above. It is strange that whilst the order seems to have found a rendezvous in Tonga, no one except Horne appears to have recorded any of the genera from Samoa. They are fairly well represented in Fiji; but it is in Tonga that we especially note the gathering together of several Sapotaceous trees with large heavy seeds, of the genera Bassia, Mimusops, and Sideroxylon. Besides owning one or two species of Sideroxylon in common with Fiji (Burkill), this small group possesses Bassia amicorum and Mimusops kauki, both of which were found there by Forster at the time of Cook’s visit. In a list of a small collection of plants made by him in Upolu in the Samoan Group about 1879, Horne includes two species of Sideroxylon (Year in Fiji, p. 286); and according to Seemann there is a Sapotaceous tree in Wallis Island. A species of Bassia exists in Rarotonga, the seeds of which, from Mr. Cheeseman’s description of the fruit, must be almost an inch long. Drake del Castillo refers to an endemic Tahitian tree near Mimusops; but its fruit was not known to him.

As already indicated, the difficulties connected with the Sapotaceæ affect the whole Pacific from New Zealand north to Hawaii and from Fiji east to Tahiti. We are driven to appeal to the agency of frugivorous birds, at least in the case of Sideroxylon, since some fruits experimented on by me in Fiji sank at once or in a day or two, the seeds having no buoyancy. That birds actually disperse the seeds of this and other genera of the order has been already pointed out, yet it is possible that currents have at times aided in the dispersal of some of the genera. This is indicated by the circumstance that, as we learn from Schimper, some Sapotaceous trees are to be included in the Malayan strand-flora, namely, Sideroxylon ferrugineum, Mimusops kauki, and M. littoralis, all occurring as well on the Asiatic mainland, the first growing also in the Liukiu Islands, and the last in the Andaman and Nicobar Groups.

Ruppia maritima (Potameæ).—This cosmopolitan aquatic plant has only been recorded in Polynesia from Hawaii, Samoa, and Fiji. It had not been collected in Fiji before my discovery of it in 1897. Amongst other oceanic islands where it occurs may be mentioned the Bermudas, where, according to Hemsley, it exists as an indigenous plant in the lagoons. Chamisso first noticed it in Hawaii, and Hillebrand remarks that it grows in shallow waters along the coasts. Amongst other localities where I noticed it in this group may be mentioned the north-west coast of the large island of Hawaii between Kailua and Keahole Point. Here in 1896 it was thriving in brackish-water ponds, with Sesuvium portulacastrum growing at the edges. Reinecke observes that it occurs in similar ponds in Samoa. In 1897 I found it in abundance in the Rewa estuary (Fiji), both in the creeks and in the main channel. In the following year it was not to be found in this locality, a circumstance noticed both by the natives and by resident whites. The fruits of this plant possess no floating power, sinking, even after prolonged drying, in a few hours. It is to ducks and to birds of similar habit that its dispersal must be attributed.

THE ABSENTEES FROM HAWAII.

It has been before remarked that of the 330 or 340 genera of flowering-plants recorded from Fiji some 200 are not known in Hawaii. It will only be possible to deal with the absent genera in a cursory manner; but enough will be done to show that we are face to face here with a multitude of the seeming inconsistencies that so often beset the study of plant-distribution.

A host of plants are unrepresented in Hawaii, of which it may be said that their seeds or fruits are not less suited for being carried across the Pacific than those of many that are now in that group. On the other hand, a number of genera exist there which we should never expect to have been endowed with the capacity, and to have received the opportunity, of crossing nearly 2,000 miles of ocean. Yet perhaps when Nature acts in a wholesale fashion and excludes entire orders we may be able to perceive the dim outlines of a principle of exclusion at work. But even here much caution and some clearing of the ground are needed.

For example, having regard to the several modes of dispersal possessed by the great variety of fruits and seeds of the Sterculiaceæ, it would be almost meaningless to remark that the order so well represented in Fiji is practically non-existent in Hawaii as far as truly indigenous plants are concerned. It is true that two species of Waltheria are here present, but one of them W. americana, is a weed probably introduced by the aborigines whilst the other, W. pyrolæfolia, recorded from a solitary locality by the Wilkes Expedition, has seemingly never been found since. From the standpoint of dispersal the genera Sterculia, Heritiera, Kleinhovia, Melochia, and Commersonia, that are represented in Fiji but not in Hawaii, cannot be discussed together. With Sterculia is concerned the dispersal by birds of large seeds, an inch in length, not particularly well protected, the genus being confined to Fiji alone of all the oceanic Pacific groups. Heritiera is only represented by a littoral species, the large fruits of which are carried great distances by the currents; and no other agency of dispersal is here possible. The last three genera are distributed over the South Pacific, their relatively small seeds being probably in the main dispersed by granivorous birds; whilst the setose fruits of Commersonia may have been at times transported in birds’ plumage.

It is more legitimate, perhaps, to speak collectively of the orders Meliaceæ and Melastomaceæ as absent from Hawaii; but even here the issue raised is one concerned rather with opportunities than with capacities for dispersal. Several years ago, M. Casimir de Candolle remarked that “it is hardly credible that the Meliaceæ should be entirely absent from the Sandwich archipelago” (Trans. Linn. Soc. Bot., vol. i. 1880). Yet it can scarcely be said that this is a matter connected with means of dispersal. Amongst the Meliaceous genera represented in Fiji, Vavæa and Aglaia have a berry, Melia has a drupe, and Dysoxylum has a capsule. So again with the Melastomaceæ; it possesses at least six genera in Fiji, two in Tahiti, and none in Hawaii. Whilst the genera Melastoma and Medinilla have baccate fruits with minute seeds, Astronia has a capsule with similar seeds, and Memecylon has a single-seeded berry. Since, however, minute seeds are most typical of the order, those of Melastoma denticulatum being about one-fiftieth of an inch or ·5 mm. in size, it would seem that this character has not aided its dispersal in the Pacific so far as Hawaii is concerned. From the circumstance that berries, drupes, and capsules are represented in these two Fijian orders we may form the opinion that their non-occurrence in Hawaii is due not so much to lack of capacities for dispersal as to failure of opportunities.

This opinion is much strengthened when we come to deal with the individual genera, where the predominant cause of the absence of so many Fijian genera from Hawaii is concerned with the failure of the agencies of dispersal. It is not a question of a difference in size between the groups, since, although the surface-area is approximately the same in both groups, Hawaii possesses only two-thirds of the number of genera occurring in Fiji. It is not a question of capacity for dispersal across an ocean, since birds have transported across the Pacific to Hawaii the “stones” and large seeds of genera like Elæocarpus and Sideroxylon, a feat that would have been deemed impossible by many botanists. It is no lack of capacity for dispersal that has excluded Loranthus from Hawaii and has admitted Viscum.

Few genera, indeed, would seem to be better fitted for dispersal by frugivorous birds in the Pacific than that of Ficus. Its fruits are known to be eaten by birds all over the area of the genus; and we find the species distributed over the South Pacific from Fiji to Tahiti, but they are quite absent from Hawaii. This is the more remarkable on account of the occurrence of a species of Ficus resembling a banyan in Fanning Island about 900 miles south of the group (Bot. Chall. Exped., iii. 116, 194), and because the Hawaiian Islands possess the Meliphagidæ or Honey-eaters, which are widely distributed in Polynesia and are known to feed on these fruits—a matter further discussed in my treatment of Ficus later on in this chapter.

Of several Rubiaceous genera with fleshy fruits that are represented both in Fiji and Tahiti, such as Stylocoryne and others, and of those Rubiaceous genera with minute seeds that, like Ophiorrhiza, are distributed over the South Pacific, none occur in Hawaii. Here we find represented other genera of the order, like Gardenia, Plectronia, and Coprosma, that do not appear to be better fitted for dispersal by frugivorous birds than many of the genera not existing there. If birds have carried to Hawaii in their plumage the fruits of Pisonia and Sicyos, it cannot be merely a question of capacity for dispersal that is concerned with the restriction to the South Pacific of genera with hairy seeds, such as Trichospermum, Alstonia, and Hoya.

It is unnecessary to dwell longer here on the subject of the Hawaiian absentee-genera, since many of the absent plants will be discussed when dealing with the peculiarities of the Fijian flora. The data there given all go to show that mere lack of capacity for dispersal over the Pacific often counts for little in supplying us with an explanation of the absence of so many likely genera from the Hawaiian flora. Hawaii has only been stocked with those genera common to Fiji and Tahiti that could have reached it during each age of general dispersal over the Pacific. In later eras the dispersing agencies have been mainly active in the tropical South Pacific; and thus it is that, as will be pointed out in a later page, the bulk of the plants of the Malayan era are confined to the region between Fiji and Tahiti. In a still later period the dispersing agencies have confined their operations mainly to Western Polynesia and the last immigrant genera have not reached beyond the Fijian region.

The whole story of plant-life in the tropical Pacific is bound up with these successive stages of decreasing activity of the dispersing agencies. The story of plant-distribution in this region is well illustrated in its earlier phases of general dispersion in the floral history of Hawaii, in its later phase by those Asiatic genera that have only crossed the South Pacific to Tahiti, and in its last phase by those genera that have never extended beyond the groups of the Fijian area. The area of active dispersion, that first comprised the whole of the tropical Pacific, was afterwards restricted to the South Pacific, and finally to the western portion of that area. It can scarcely be doubted that these successive stages in the contraction of the area of active dispersion of plants in the Pacific were accompanied by a corresponding diminution in the general distribution of birds in the same ocean, to which it stood in the relation of an effect to a cause.

TAHITI.

The peculiarities of the Tahitian flora as compared with Hawaii and Fiji may be discussed by treating first those genera that are alone represented in Tahiti, the “residual” genera; then those that it possesses in common first with Hawaii and then with Fiji; and lastly by pointing out the more noticeable gaps in the flora. By Tahiti is typically signified the whole Tahitian region, which includes the Austral and Cook Groups, the Society Islands, the Paumotus, and the Marquesas.

THE TAHITIAN RESIDUAL GENERA.

The non-endemic genera occurring alone in the Tahitian region and not found either in Hawaii or in one or other of the three groups of the Fijian region (Fiji, Tonga, Samoa) are not more than half a dozen. These six genera are exceedingly interesting; but since each tells a different story and gives its own independent indication they cannot be treated in a collective sense. Nor are they all to be regarded as anomalies in plant-distribution, since with a single exception there is scarcely one concerning which it is not in some way possible to give an explanation of its isolation without coming into conflict with the principles of plant-dispersal. The exception is Lepinia tahitensis, which, without presenting any very evident capacity for dispersal, has not been recorded from any other localities in the Pacific than the far-separated Solomon and Tahitian Groups. There is a suspicion that, as in the case of the residual genera of Hawaii, America may have contributed some of the original plants, since three of the genera, Buttneria, Coriaria, and Bidens, occur in that continent, and in the case of Coriaria Tahiti possesses a species found in South America as well as in New Zealand.

One of the trees in question is Cratæva religiosa, an Asiatic species, which may be placed among a group of trees, including Cananga odorata and Fagræa Berteriana, which, whilst they are much esteemed by the inhabitants of the South Pacific for their fruits or their flowers, and are often planted in and around their villages, possess fruits that attract birds, and in the case of Cananga are known to be dispersed by fruit-pigeons. Probably the aborigines and the birds have worked together in the distribution of these trees.

The genera Buttneria of the Sterculiaceæ and Berrya of the Tiliaceæ are represented in this region by species that must owe their dispersal to birds, though I have no data relating to the matter of their dispersal, their fruits being capsular, in the first case prickly. Coriaria is a mountain genus in Tahiti and will be found discussed in Chapter XXIV. in connection with the Tahitian mountain-flora. Its absence from the West Polynesian groups is no doubt to be connected with their insufficient altitude. In addition to the introduced Bidens pilosa, a common tropical weed, Tahiti possesses two other truly indigenous species of Bidens, of which one at least is peculiar to the region. The achenes of this genus are well known to be adapted for dispersal in a bird’s feathers; and since the genus has its principal home in America, no other indigenous species having been recorded from South Polynesia, it is not unlikely that the parent species was American.

One of the numerous enigmas of the Pacific floras is concerned with the presence in the islands of Tahiti and Moorea (Eimeo), in the Society Group, of the Apocynaceous tree, Lepinia tahitensis. The genus contains this solitary species, which has been collected only in one other locality, namely, in the Solomon Group, where it was obtained by the Rev. R. B. Comins. Such an instance of disconnected distribution is rare in the Pacific Islands, and undoubtedly it represents one of the difficulties of the Tahitian flora. The fruits, which are indehiscent and five or six inches in length, possess a fibrous pericarp and a single seed. No data are to hand relating to the capacities for dispersal possessed by this plant, but it is certain that it has had some means of crossing the sea between the adjacent islands of Tahiti and Moorea. (See Hemsley, Journ. Linn. Soc. Bot., xxx. 165.)

TAHITIAN GENERA FOUND IN HAWAII TO THE EXCLUSION OF FIJI.

This subject has been already discussed in this chapter in dealing with the genera restricted to Hawaii and Tahiti.

TAHITIAN GENERA FOUND IN FIJI TO THE EXCLUSION OF HAWAII.

Excluding the orchids, sedges, and grasses, as well as the few endemic genera, between sixty and seventy genera, or rather less than half of the genera of the flowering-plants of Tahiti, are found in Fiji to the exclusion of Hawaii. Of these, rather over a half are Old World genera; about a third occur in both the Old and the New World; four are confined to Polynesia, and not one is exclusively American. One-third are genera now possessing in the Tahitian region endemic species either entirely or in part, and in such cases we may consider that the agencies of dispersal are now inactive or partially suspended; the others belong entirely to the present era of dispersal. About half have more or less fleshy fruits fitted for dispersal by frugivorous birds. About a fourth have capsular or other dry fruits that must have been also dispersed by birds preferring a drier diet. Three only possess hairy seeds or fruits suitable for being carried in a bird’s plumage, namely, Commersonia, Weinmannia, and Alstonia. There remain about a fourth of the total that are shore-plants dispersed by the currents, being in two cases (Ximenia and Kleinhovia) assisted by birds; whilst Triumfetta, another littoral genus, is probably distributed by birds alone.

There are no cases of special difficulty from the standpoint of dispersal in these sixty and odd non-endemic genera that Tahiti possesses in common with Fiji to the exclusion of Hawaii. The lack of difficulties connected with the dispersal of all these Tahitian genera is worthy of note, because there are very few difficult genera amongst the rest of the Tahitian flora. Excluding Lepinia tahitensis, which has been already referred to, there are scarcely any “impossible” plants in the Tahitian region; and even in this case, when the modes of dispersal of Lepinia come to be investigated, it is likely that much of the difficulty will disappear. Hawaii, as we have before seen, abounds with perplexing questions of this nature. When dealing with the absentee Tahitian genera, later on in this chapter, it will be shown that “size” has played a prominent determining part in the exclusion of genera from Tahiti, genera with seeds or “stones” exceeding half an inch or twelve millimetres in dimension being, as a rule, unrepresented amongst the truly indigenous plants.

My further remarks on these Tahitian genera found in Fiji but not in Hawaii will be limited to some general observations from the standpoint of dispersal. I will first discuss some of those genera that possess only peculiar species. They belong to an era of dispersal that, as far as Tahiti is concerned, is passing or has passed away. Here we have the species of each genus more or less localised in the various South Pacific archipelagoes; but, as with Meryta, Alstonia, and Loranthus, it is often apparent that, although the Tahitian region is mainly outside the zone of present dispersal, the different groups of the Western Pacific are kept in touch by the possession of species in common. This testifies to the activity of dispersal in that region after it had become suspended in Eastern Polynesia. The connection between the isolated endemic species of Eastern Polynesia and a species ranging over the Western Pacific can sometimes be shown, as in the case of Loranthus, where a species confined to the Society Islands and to the Marquesas is very closely related to L. insularum, a widely-ranging West Polynesian species that reaches eastward as far as Rarotonga.

We next have those genera like Grewia, Nelitris, Melastoma, Randia, Geniostoma, Tabernæmontana, Fagræa, Bischoffia, Macaranga, and Ficus, that possess in Polynesia one or more widely-ranging species. The agency of the polymorphous species, which I have described in the preceding chapter in connection with the general dispersal of Malayan plants over the whole of Polynesia, is evidently also active when the work of dispersal is restricted to the South Pacific. Its operation is to be distinctly traced in all the genera above named except in Fagræa and Ficus. Thus, in the genera Grewia, Melastoma, Randia, Geniostoma, and Macaranga we find a single variable species ranging over the South Pacific from Fiji to Tahiti, keeping all the groups in touch, but associated in each, as a rule, with one or more peculiar species. A yet earlier stage in the process is to be seen in those genera which, like Nelitris, Tabernæmontana, and Bischoffia, possess only a solitary species ranging over the South Pacific, varying in each group, but not usually associated with endemic species. As with Melastoma, Macaranga, and others, we can often trace the widely-ranging species of Polynesia back to its home in Malaya, and with these and other genera the connection between a species confined to a group and a variable species ranging through all the archipelagoes of the South Pacific can sometimes be detected in the affinity of their characters.

It is thus seen that one of the principal determining causes of the differentiation of species in Polynesia lies in the failure of the dispersing agencies, a widely-ranging species becoming in consequence gradually isolated in the various groups. With some genera, as with Ophiorrhiza, it is possible to show that the resulting endemic species pass into each other by intermediate forms.

My further remarks on the Tahitian genera occurring in Fiji but not in Hawaii will be devoted mainly to those with which I was most familiar from the standpoint of dispersal.

The Tiliaceous genus GREWIA offers a good example of those Polynesian genera which possess in the South Pacific a single widely-ranging species associated often with endemic species in the individual groups. It is likely that a polymorphous form, including most of the Polynesian species, could be here constituted. The fruits are dryish drupes, becoming black and moist when over-ripe, and containing three or four pyrenes suitable for distribution by birds and five or six millimetres in size.

The berries of NELITRIS, a genus of the Myrtaceæ, contain a few hard seeds that are well fitted for dispersal by frugivorous birds. I am inclined to follow Drake del Castillo, who considers that there is only one varying species, N. vitiensis (Gray), which is distributed over the whole of the South Pacific from the Solomon Islands to Tahiti. The tendency of this widely-ranging species to vary in different groups is indicated in the fact that some botanists have distinguished other species within these limits. It is noteworthy that N. paniculata in Indo-Malaya and N. vitiensis in the Pacific cover the whole range of the genus. It would be interesting to establish a connection between them.

MELASTOMA, an Old World genus of forty and more species, has one very variable species, M. denticulatum, which, as defined by Bentham, has the range of the genus from tropical Asia across the Pacific to Tahiti. This plant is associated in some groups, as in Fiji, Tonga, and Samoa, with other more or less localised species, and it affords a good example of the principle of polymorphism in species-making. The berry-like fruits contain an abundance of minute seeds, half a millimetre in size, which, when rendered adhesive by adherent pulp, might readily stick to feathers, or they might pass unharmed through the alimentary canal of a bird. It is noteworthy that amongst the plants regarded by Prof. Penzig as introduced by frugivorous birds into Krakatoa since the eruption is a species of Melastoma.

Few genera in these islands would better repay a careful study of their species with regard both to the influence of station on specific characters and to the question of “mutations” than OPHIORRHIZA. I found the three Fijian species of this Rubiaceous genus so often in close association, that I cannot doubt there is some connection between them. Seemann and Gray, indeed, characterise two of them as confluent species. The island of Tahiti alone possesses five peculiar species, and it is evident that this island has been a centre of development for species of Ophiorrhiza, just as Samoa has become the birthplace of many species of the Urticaceous genus Elatostema. The minute angular seeds of Ophiorrhiza would probably be transported in a bird’s feathers or in adherent soil. As my experiments showed, they do not become adhesive when wet.

The genus LORANTHUS as distributed in the South Pacific has already been briefly noticed. There is a species confined to the Tahitian region, and there is another peculiar to Samoa, whilst one widely-ranging species, L. insularum, that connects these regions together, reaching east to Rarotonga, is closely related with the Tahitian species. There was no doubt originally a single polymorphous plant that ranged over the tropical South Pacific. With regard to the mode of dispersal of the seeds of this genus of parasites, I should at once refer to the systematic and careful observations made by Mr. F. W. Keeble in Ceylon (Trans. Linn. Soc., v. 1895-1901). He formed the opinion that the seeds of Loranthus usually reach their host without passing through the alimentary canal of a bird, being merely wiped off its bill. This method would never carry the seeds to Tahiti or even to Fiji; and since this observer remarks that, although most of the seeds in the droppings were completely rotten, some of them “possibly pass through the gut uninjured,” we may accept this possibility as sufficient for the purpose of dispersal in the Pacific Ocean. Mr. Keeble notes the observation in Teil 3 of Engler’s Die Natürlichen Pflanzenfamilien that the seeds may germinate after passing through a bird’s intestine; and we may therefore infer that whilst the method he describes is typical of local dispersal, the other method is required in the instance of oceanic dispersal.

ALSTONIA, an Apocynaceous genus of tropical Asia and Australia, yields the caoutchouc of Fiji. Besides possessing in Fiji and Samoa peculiar species, the islands of Western Polynesia have in A. plumosa a species common to Fiji, Samoa, and New Caledonia. Another species, A. costata, is restricted to Eastern Polynesia, occurring in the different islands of the Tahitian Group as well as in Rarotonga. It is possible that the Pacific species may be connected with A. scholaris, a species possessing the range of the genus with the exception of Polynesia. The long ciliated or hairy seeds, six to nine millimetres in length, are fitted for transport by the winds and in birds’ plumage. The follicles dehisce on the tree, and, according to Horne, the light seeds are distributed locally by the wind. It is probable that the thick white juice oozing from a broken branch would at times aid the adhesion of the seeds to a bird’s feathers.

GENIOSTOMA, a genus of the Loganiaceæ, is found in Malaya, Australia, and New Zealand. It possesses in G. rupestre a species that ranges across the South Pacific from New Caledonia to Tahiti, being associated with one or more endemic species in most of the groups. The fruit is a dehiscent capsule containing numerous small seeds imbedded in a yellowish pulp; and from the standpoint of dispersal it may be placed in the same category with Pittosporum and Gardenia (see pages 310, 313).

The same principle involved in the occurrence of a species ranging the South Pacific from New Caledonia to Tahiti, and associated with one or more endemic species in most of the principal groups, is illustrated in the Euphorbiaceous genus MACARANGA. It is specially noteworthy that M. tanarius, which ranges from India to East Australia and the New Hebrides, comes in touch in the group just named with M. harveyana, the widely-ranging plant of the South Pacific above alluded to, and itself an Asiatic species (see Burkill; Bot. Chall. Exped., iii. 191; Index Kewensis). The connection between M. harveyana, the widely-ranging species of the South Pacific, and the endemic species in the various groups is indicated by its affinity with M. reineckei, a Samoan species. The Macarangas in Fiji grow in a variety of situations, on the borders of estuaries, in the mountain forests, and on the isolated mountain peaks. It is to birds that we must look for the dispersal of the genus. In the case of a species, apparently M. seemanni, common in the Rewa delta, the seeds, which soon fall out of the cocci, are not infrequently found in the drift of the estuary, but they sink in a week or two. Other species examined showed no capacity for dispersal by currents. The fruit of M. harveyana is provided with a few prickles, but since it breaks up into the cocci, from which the seeds soon fall out, these appendages could scarcely aid its dispersal.

Like many other genera, TABERNÆMONTANA, an Apocynaceous genus distributed through the tropics, is represented in Polynesia by a widely-ranging species, T. orientalis, which extends from Malaya and Eastern Australia through all the large groups of the South Pacific from the New Hebrides to Tahiti, and is associated in Fiji with one or two peculiar species, one of which, according to Mr. Burkill, is nearly related to it. This genus therefore seems to illustrate the earliest stage in the Pacific of that process by which a widely-ranging species takes on a polymorphous habit and through its variations gives rise to different species in various groups. Prof. Schimper ranks T. orientalis amongst the Malayan strand-flora; but in Fiji the Tabernæmontanas are only littoral where the soil is rich as in alluvial regions; and they have no capacity for dispersal by currents that is worth speaking of, the seeds in the case of T. orientalis and another species sinking after drying for years, whilst the follicles soon open in water and go to the bottom in a few days. The observations of Gaudichaud and Moseley indicate that some Malayan species are dispersed locally by the currents (Bot. Chall. Exped., iii, 279, 293); but the fruits of the genus are evidently quite unfit for oceanic dispersal by this agency. We find in the bird the agent that has carried the genus to the distant island-groups of the Pacific; and from the standpoint of dispersal the fruits may be placed with those of Pittosporum and Gardenia, being follicular, and in the Fijian plants possessing seeds, 5 to 10 millimetres in size, embedded in a pulp.

FAGRÆA, an Asiatic and Malayan genus of the Loganiaceæ, is represented in the Pacific by F. berteriana ranging through all the groups and islands of the South Pacific from the Solomon Islands and New Caledonia to Tahiti and the Marquesas, and by one or two other species in Fiji. It is with Fagræa berteriana that we are entirely concerned. The tree is often planted by the Pacific islanders near their villages; and since they value its timber and use its large fragrant flowers for personal decoration and for other purposes, it is probable that they have aided in its dispersal. But, as shown below, it behaves in most localities as an indigenous plant; and its berries are well fitted for promoting its dispersal by frugivorous birds.

I was familiar with Fagræa berteriana both in the Solomon Islands and in Fiji; and in the last-named locality I especially studied it from the standpoint of dispersal. All over the South Pacific, whether in the Solomon Islands, in Fiji, in Rarotonga, or in Tahiti, this tree, though thriving also in the lower levels, especially frequents rocky scantily vegetated or open-wooded hill-tops and crests up to 2,000 or 2,500 feet above the sea. In the rich alluvial soil of the Rewa delta in Fiji it attains a height of 25 or 30 feet or more, whilst in the poor, dry soil of the “talasinga” plains in this group it is much dwarfed, and often does not exceed 10 feet, and may be only 6 feet high. It is in these “talasinga,” or “sun-burnt,” plains of Fiji, especially in the Mbua province of Vanua Levu, that the tree, although dwarfed, seems most at home. Here it flowers and fruits abundantly whilst associated with Acacia, Casuarina, and Pandanus trees, and it is in such dry localities that this tree reflects in its choice of station the behaviour of different species of the genus in the Malay Peninsula, where they grow in open heath-country and sometimes on sandy heaths (Ridley in Trans. Linn. Soc. Bot., iii, 1888-94). The fruits and seeds of F. berteriana have little or no capacity for dispersal by currents. On the Fijian plains the berries partially wither and rot on the tree. In the western part of its area this tree almost comes in touch with the Asiatic species, F. obovata, that ranges from India and Ceylon to the Malayan region, a species that must be indebted to frugivorous birds for its wide distribution.

The Euphorbiaceous genus BISCHOFFIA seems to offer another example of polymorphism in a wide-ranging species. Following Drake del Castillo, I take the genus as including only a single species, B. Javanica, a tree distributed over tropical Asia, Malaya, and Polynesia as far east as Tahiti. The variable character of the species is indicated by the different views held by the several botanists who have discussed the South Pacific species. Whilst it is a common forest-tree in Indo-Malaya, it affects in the Pacific islands the open-wooded districts of the lower levels, and it is not uncommon on the dry “talasinga” plains of Fiji. The fruits and seeds displayed in my experiments little or no capacity for dispersal by currents; nor do these dryish berries, with seeds four or five millimetres long, seem to be especially attractive for fruit-eating birds; and it is likely that the same birds that distribute Macaranga seeds also disperse those of this genus. The tree bears the same name over the South Pacific, “koka” in Fiji and Rarotonga, and “oa” in Samoa. Like many other Polynesian trees, it has its uses, but there is no reason to believe that the natives have aided materially in its dispersal.

FICUS, a large genus comprising several hundred species, attains its greatest development in tropical Asia and in Malaya. It is well represented in the Western Pacific from the Solomon Islands to Fiji and Samoa; but in Eastern Polynesia the species are very few, and the genus is altogether absent from Hawaii, although a species has been found in the North Pacific in Fanning Island, about 900 miles south of the Hawaiian group (see page 377).

The Polynesian species are for the most part restricted to the Pacific islands, but there are only two species that range over the South Pacific as far east as Tahiti, namely, Ficus prolixa, the Tahitian banyan, and F. tinctoria. Some species are confined to Western Polynesia, such as F. obliqua, the Fijian banyan, F. scabra, and F. aspera, the last occurring in East Australia. Among the individual groups Fiji possesses probably fourteen or fifteen species, of which, perhaps, a third would be peculiar. According to Dr. Warburg, as cited in Dr. Reinecke’s paper, Samoa owns eight species, of which six may be endemic. In Rarotonga and Tahiti we find only F. prolixa and F. tinctoria. The species in the groups where they are best represented belong to three or four sections of the genus.

The banyans of the South Pacific are represented by three or four species, namely, Ficus prolixa, the Tahitian banyan, found all over the tropical groups of the South Pacific from the New Hebrides and New Caledonia to Tahiti, the Marquesas and Pitcairn Island (Maiden); F. obliqua, the Fijian banyan, confined to the islands of the Western Pacific from the New Hebrides to Tonga; and two new banyans in Samoa, as described by Dr. Warburg in Dr. Reinecke’s paper. In my paper on Polynesian plant-names it is shown that the banyans possess two names in the Pacific, one being “aoa,” the Polynesian name, found in all the groups from Samoa eastward, and connected linguistically with the Malayan and Malagasy banyan-words; the other, the Melanesian name typified in the Fijian “mbaka,” and represented in a variety of forms in the New Hebrides and neighbouring groups.

It is probable that the Pacific islanders have assisted in the dispersal of one or two of the species of Ficus, such as F. tinctoria, which they employ for different purposes, but, generally speaking, birds are active agents in distributing the genus. I need scarcely say that the agency of the currents is quite insufficient to explain the distribution of Ficus. When in Fiji I experimented on three or four different species of Ficus belonging to the sections of the genus there represented. The fruits may float at first, but within a week or ten days they break down, and the seeds escape and sink. Beneath a tree of F. scabra growing on the banks of the Wai Tonga in Viti Levu, I noticed a number of its fruits floating in a sodden condition among the reeds at the river-side.

It is with the banyans that the dispersal of the seeds by frugivorous birds becomes most evident. This is at once indicated by the frequent occurrence of these trees in the interior of coral islets in the Western Pacific, as in Fiji and in the Solomon Islands. Fruit-pigeons roost in their branches, and birds shot on these islets often contain the fruits in their crops (Bot. Chall. Exped., iv, 310). The process may also be seen in operation in Krakatoa. Professor Penzig found in 1897 that three species of Ficus had established themselves there since the eruption of 1883 through the agency of frugivorous birds. Besides pigeons, we find that parrots, hornbills, honey-eaters, &c., feed on these fruits, and I possess a large number of references to this subject. The Messrs. Layard in New Caledonia, Dr. Meyer in Celebes, Mr. Everett in Borneo, Dr. Forbes in Sumatra, and several other contributors to Ibis might be here mentioned. Dr. Beccari, in his Wanderings in the Great Forests of Borneo, speaks of “the facile dissemination of the various species of Ficus through the agency of birds,” and he arrives at certain important conclusions which are discussed in Chapter XXXIII.

I have before alluded to the absence of Ficus from Hawaii. This group possesses the Honey-Eaters (Meliphagidæ), birds well suited for dispersing species of Ficus over Polynesia; but this family of birds is only represented by peculiar genera in Hawaii, and therein lies the explanation. At the time when the Honey-Eaters roamed over Polynesia, the genus Ficus had not arrived from Malaya. The connection between the bird and the plant is well shown on Fernando Noronha, which possesses a peculiar species of Ficus and a peculiar species of dove, the only fruit-eating bird in the island (Ridley).

THE ABSENTEES FROM TAHITI

Generally speaking, all the “difficult” genera which puzzle the student of plant-dispersal in Fiji and Hawaii are absent from the Tahitian region. Those with stone-fruits and with large seeds, where the stone or seed is an inch in size and over, are absent from Tahiti. Thus the genera Canarium, Dracontomelon, Myristica, Sterculia, and others, of which the three first-named are known to be dispersed by fruit-pigeons, have not advanced into the Pacific eastward of the Fijian region. We miss in the Tahitian islands the large-fruited palms of Fiji, such as the Veitchias with fruits two to two and a half inches (5 to 6 cm.) long, and we find in their place a Ptychosperma, evidently very rare, and the widely spread Pritchardia pacifica, that may have been introduced by man, both with drupes not far exceeding half an inch (1·2 cm.) in size. The islands of the Tahitian region also lack the Coniferæ; and genera like Dammara, Dacrydium, and Podocarpus that give such a character to the Fijian forests are not to be found. In this region we do not find many of the large-seeded Leguminous genera, such as Cynometra, Storckiella, and Afzelia, that occur in Fiji, the only large-seeded genera that it possesses being such as are brought by the currents, namely, Mucuna, Strongylodon, Cæsalpinia. The difficulties presented by the occurrence of the inland species of Canavalia and Mezoneuron in Hawaii do not offer themselves in Tahiti (see Chapter XV). Tahiti also lacks, as often before observed, the mangroves and most of the plants of the mangrove-formation.

As above remarked, the Fijian trees with large “stones” and heavy seeds an inch in size are not to be reckoned amongst the indigenous Tahitian plants, “size” being an important determining factor in the exclusion. The occurrence of Elæocarpus in Rarotonga presents no real difficulty, as I have explained in Chapter XXVI. An apparent exception is presented by the existence in Tahiti of Calophyllum spectabile, where the stones are about an inch across; but since its fruits can float in sea-water for nearly a month, and on account of the value placed on its timber by the Polynesians, we cannot altogether exclude the agencies of man and the currents. One seeming exception is also offered by the presence of Serianthes myriadenia, a tree which in Fiji grows both in the forests and on the banks of the tidal estuaries. Its seeds, which are six to seven-tenths of an inch (15 to 18 mm.) in length, have no buoyancy, and the pods float only two or three weeks. The case of Lepinia tahitensis is alluded to elsewhere, but it may be added that these and other difficulties await further investigation.

A great many Fijian plants are not found in the Tahitian region, such as Micromelum, those of the order Meliaceæ, the Melastomaceous genus Medinilla, Myrmecodia, Ophiorrhiza, &c., which are often quite as well fitted for over-sea transport as are several of the plants already established there. But it should be remembered that crowding out would often come into play in such a contracted region. The area, however, has been very generously dealt with as regards plant genera. Though the total land-surface cannot be more than one-fourth or one-third that of Fiji or Hawaii, it possesses more than half the number of genera found in Fiji, and four-fifths of the number found in Hawaii.

FIJI

The Fijian Genera not found in either the Tahitian or Hawaiian Regions

We have already in some degree dealt with Fiji in so far as the partial dispersal of genera over the Pacific islands is concerned. We have seen that it possesses very few genera (not a score in all) in common with Hawaii that are not found in the Tahitian region, and it is assumed that in most cases such genera reached Hawaii independently and not through the South Pacific. On the other hand, excluding the grasses, sedges, and vascular cryptogams, Fiji owns in common with Tahiti between sixty and seventy genera that do not occur in Hawaii. This shows unmistakably the trend of plant migration in the Pacific islands. Several interesting features in plant-distribution have been already brought out, and notably the fact that Indo-Malayan genera with large seeds or “stones” an inch in size have been arrested in the Fijian region in their passage into the South Pacific. Thus Canarium, Dracontomelon, Myristica, and Sterculia have not extended eastward of the Fijian area.

Yet a very large proportion of the Fijian genera, quite half of the total number, are not represented either in the Tahitian or in the Hawaiian region; and of many of them it is obvious that they are as well fitted to be carried over the Pacific as are those that have actually reached Tahiti and Hawaii. Take, for instance, Begonia, which has not extended east of Fiji, though Hillebrandia, a genus of the order, is peculiar to Hawaii. Nor can we explain why with three genera like Geissois, Dolicholobium, and Alstonia, possessing seeds dispersed by the winds, only the last-named has passed beyond Fiji. However, as before remarked, it is probable that lack of opportunity rather than capacity for dispersal has determined the matter, and we must, therefore, assume that many of the genera have halted in the Fijian region because they entered the Pacific after the age of active general dispersal over that ocean.

Occasionally we notice in this region that which we have observed in the case of Cyrtandra in different Pacific groups, namely, a sudden development of what Hillebrand terms “formative energy” in a genus, such as we find in the case of Elatostema in Samoa, and in that of Psychotria in Fiji and Samoa. The principle of polymorphism in the development of species is also illustrated by Micromelum and by Limnanthemum. In the last case we possess a typical polymorphous species in Limnanthemum indicum that has played in this respect the rôle of Naias marina in the warm waters of the globe.

With several genera that like Gnetum, Myristica, and Sterculia occur both in the Old and the New World, it is evident that in explaining their distribution we are dealing with something more than questions of means of dispersal. With these genera, and with others like Lindenia, it seems almost futile to talk of means of dispersal, when to all appearance their existing distribution is but the remnant of an age of general dispersion over the greater part of the warm regions of the world. These genera, with others, might be cited in favour of the continental hypothesis relating to the islands of the Western Pacific. Trees with stone-fruits, such as Canarium, Couthovia, Dracontomelon, and Veitchia, where the stones are an inch and more in length, might be also adduced by some in evidence of this theory. But in these cases the lesson of Elæocarpus (Chapter XXVI) should always be remembered, since the “stones” of drupes may vary greatly in size amongst the different species of a genus, and species seemingly “impossible” from the standpoint of dispersal in one group may be represented in other groups by species where the size of the “stone” presents no difficulty in attributing the dispersal of the genus to frugivorous birds.

Sterculia

The problem connected with the presence of this genus in Fiji is but a part of the still more difficult problem connected with the dispersal of the genus over the tropics. The riddle presented by the Fijian species seems, indeed, difficult enough; but it merely presents in miniature the great mystery surrounding the whole genus. According to the Index Kewensis no other species have been found in oceanic islands except those occurring in the Western Pacific, as in Fiji, the New Hebrides, and New Caledonia, and most of these seem to be confined to those islands. We have here a genus that repeats the Dammara difficulty of the Western Pacific.

The trees are common in places in the Vanua Levu forests, where the large, woody, open follicles may be seen lying in numbers on the ground, empty and in all stages of decay. The seeds of one species, near Sterculia vitiensis, were nearly an inch long and sank like stones. The unopened follicles will float for weeks; but it is evident that Nature does not disperse the genus in this fashion, since the fruits before dehiscence remain on the tree. It is also noteworthy that Gaudichaud, when describing the floating drift of the Molucca seas, refers to the open follicles of two or three species of Sterculia (Bot. Chall. Exped., iii, 279). The fruits never came under my notice in the drift of Fiji. The seeds of a Fijian species examined by me were four-fifths of an inch (2 cm.) long. They had a thin, brittle, outer skin and crustaceous inner test, and, being edible, might attract birds; but such birds would be ground feeders, like the Megapod, and the Goura pigeon of New Guinea, and the Nicobar pigeon, birds of this habit being rare in Fiji. I should doubt whether the seeds are sufficiently protected to be preserved from injury in a bird’s stomach during a long sea-passage; and they may thus be placed in the same category with the seeds of Myristica, a genus that has also failed to reach Tahiti and Hawaii.

But the distribution of Sterculia raises other more important questions than that connected with its occurrence in Fiji, which involves an over-sea passage of only 500 or 600 miles. As in Podocarpus amongst the Coniferæ, which has a similar distribution in the Western Pacific, we have to explain the existence of the genus in the three great continental masses of Africa, Asia, and America, now separated by oceans several thousands of miles across. Here also we must look far back into the ages for a common centre of diffusion in the extreme north, such as is in a sense suggested by the occurrence of the order in the Eocene beds of Europe.

As showing unmistakably that Fiji received its species from the Old World, it may be observed that one of its trees, Sterculia vitiensis, is very closely allied to S. fœtida, widely spread in tropical Asia, in Malaya, and Australia, as well as in Africa.

Trichospermum (Sterculiaceæ)

There are only two species of this tree recorded in the Index Kewensis, one in Java, and one in Fiji as well as in Samoa. The fruit is a capsule with small, flat seeds, margined by long hairs, that might possibly attach themselves to a bird’s feathers.

Micromelum (Rutaceæ)

This small genus of tropical Asia, Malaya, tropical Australia and the islands of the Western Pacific, has one species, Micromelum pubescens, possessing the range of the genus with other species that are restricted to different localities. We thus have apparently another illustration of the part played by a wide-ranging polymorphous plant in providing new species. The red berries would easily attract frugivorous birds; but the seed-tests seem too delicate to allow the seeds to remain more than a few hours in a bird’s stomach without injury.

Cananga odorata (Anonaceæ)

This tree, which is cultivated in many places in tropical Asia and Malaya, but is certainly indigenous, according to the authors of the Flora Indica, in Ava and Tenasserim, has apparently extended into the Pacific by cultivation. But though much valued by the natives on account of its fragrant flowers, and in consequence often planted by them near their villages, it grows in some localities in Fiji and Samoa as an indigenous plant. The berries are especially suited for dispersal by frugivorous birds, their flat seeds, 8 mm. in length, possessing hard crustaceous tests that would enable them to pass unharmed in a bird’s droppings. According to Reinecke the fruits are sought after by pigeons, and particularly by Didunculus strigirostris, the Samoan Tooth-Billed Pigeon. The tree has not travelled eastward of Tonga and Samoa, with the exception of its occurrence in Rarotonga; and according to Mr. Cheeseman the Rarotongans received it from Samoa several years ago.

Geissois (Saxifragaceæ)

This genus of seven or eight known species is found in Australia, New Caledonia, the New Hebrides, and Fiji. Since New Caledonia possesses four species, it may be considered the home of the genus. To the Fijian endemic species, G. ternata, I paid special attention. The capsules dehisce on the tree and allow the small seeds to escape. These seeds, which are very light, 150 to 200 going to a grain, are 3 to 4 mm. long and are winged at one end. They could no doubt be carried some distance by strong winds; but they possess no buoyancy. Large bats probably aid in their dispersal. The Fijians assert that these animals are in the habit of visiting the trees for the sake of the honey furnished by the conspicuous red flowers. When they see a bat flying towards these trees, they are wont to remark that it is going to drink the “se ni vota,” that is, to suck the flowers of the Vota tree. It is very likely that seeds would sometimes be carried in their fur for considerable distances.

Begonia

Before the discovery of Hillebrandia, a new genus of the Begoniaceæ, in Hawaii, the order was not known from Polynesia. However, in 1878 Mr. Horne collected a species of Begonia in Fiji, and it was probably this species that frequently came under my notice in the rain-forests of the Vanua Levu mountains. In 1883 I collected a Begonia in the Solomon Islands, which I gave to Baron F. von Mueller, who informed me that it was the first record of the genus east of New Guinea, the description of Mr. Horne’s Fijian plant apparently not having been published (see Guppy’s Solomon Islands, p. 288). It is not easy to explain why a genus with such minute seeds, which are apparently as well fitted for dispersal as those of the orchids, should have such a limited distribution in the Pacific.

Dolicholobium (Rubiaceæ)

In the Index Kewensis this genus, containing five species, is restricted to Fiji. It must, however, be more generally distributed in the Western Pacific, since the genus was identified at Kew among my Solomon Island collections, and it is recorded in the list given in my book on that group (pages 283, 288, 297).

The showy, large, white, fragrant flowers of these small trees recall those of Lindenia, with which Dolicholobium is often associated in Fiji by the sides of streams and rivers. As Horne observes, the Fijian Dolicholobiums range from the sea-shores and the heads of the estuaries to the tops of the highest mountains. As noticed by me in the Solomon Islands they affected the same station, being especially common on the banks of streams. The genus has a long, narrow capsule six inches or more in length. The linear seeds, though very light, are an inch or more long, the coats being drawn out into a long tail at either end, and thus differing greatly from those of Lindenia, the other Rubiaceous genus, with which these plants are so frequently associated at the river-side. I can only suppose that the seeds are transported by the winds. The history of the genus is suggested in my remarks on Lindenia.

Lindenia (Rubiaceæ)

Respecting its distribution in the Pacific, this genus of showy river-side shrubs takes the same place amongst the plants that Galaxias takes among the fishes. It is full of mystery. Of the four species known, two grow on the river-banks of Central America and two in similar stations in the islands of the Western Pacific. Of the last-named both occur in New Caledonia, one of them being endemic, whilst the other, Lindenia vitiensis, is found also in Fiji and Samoa. Reinecke seemingly records no Samoan species, but in the list of additions at the end of his Flora Vitiensis, Seemann refers to the Fijian species as having been found in Samoa by Dr. Graeffe.

Lindenia vitiensis, as Horne aptly remarks, adorns the rocky banks of many Fijian streams with its cream-coloured flowers, which impregnate the air with their sweet odour. I found it in Vanua Levu, both at the heads of the estuaries and beside the stream and the torrent in the heart of the mountains. It was often associated with a species of Dolicholobium, which it resembled strangely in its large, showy, scented flowers and in the form of the leaf. Seemann says it is also accompanied at the river-side in Viti Levu by Ficus bambusæfolia and Acalypha rivularis. It is noteworthy that all the four plants here mentioned as being associated river-side plants in Fiji possess the long, narrow leaves of the willow type, a subject that is discussed in note 79.

The capsules of Lindenia vitiensis contain numbers of small, angular seeds about 1·5 mm. across, some 400 of them when well dried going to a grain. The seeds float buoyantly by reason of their outer covering of crisp, air-bearing, cellular tissue. When this outer covering is stripped off, the minute nucleus, or seed proper, which is barely a millimetre across and is but slightly protected, sinks at once. As the seeds float on the surface of a stream they might readily get on the plumage of an aquatic bird; but they have no special means of attachment; though, if they dried on the feathers they might adhere to some extent. That they could be carried in mud adhering to a bird across an ocean’s breadth I think most unlikely; and it should be remembered in this connection that only the dead or sickly seeds would be found at the bottom of a stream.

The most reasonable explanation of the extraordinary distribution of Lindenia is that it was in a past age found over the tropical regions of both America and the Old World, and that it has died out over the greater part of its original area. To study the means of dispersal of plants with such a distribution seems almost futile. I am inclined to think that the limited range of Dolicholobium, so frequently its station-companion in Fiji, may be similarly explained.

Limnanthemum (Gentianaceæ)

This interesting genus of aquatic plants is dispersed over the tropical and temperate regions of the globe, but with the exception of Fiji and the New Hebrides it is not found in oceanic groups, though it occurs in large continental islands like New Caledonia and Cuba. About twenty species are enumerated in the Index Kewensis, but it is stated in the Genera Plantarum that they can probably be reduced to ten, the reduction being chiefly applicable to the tropical species, nearly all of which are reducible to varieties of L. indicum, the temperate species being often very distinct. It would thus appear that although dispersal is still active in the tropics, it is in part suspended in the temperate zone, and we seem to possess in L. indicum a typical polymorphous species that has played the rôle of Naias marina in the warm, fresh waters of the globe (see page 368).

Although some of the temperate species, like Limnanthemum nymphæoides in Europe and Northern Asia, have a wide range, it is probable that this is connected not so much with means of dispersal, as with its relation to present and past drainage-areas. Rivers in the lapse of ages change their courses and carry their aquatic floras with them, leaving, however, a few of their plants around the springs and in the lakes which serve still as centres of dispersal. Rivers may even exchange their plants in flood-time in extensive level districts. Nor is the occurrence of the genus in the Old and New Worlds in the northern hemisphere to be connected with questions of dispersal across an ocean. Except in the case of small-seeded plants, like Nasturtium and Lythrum, where the dispersal could be carried on by water-fowl, the plant-species being often identical on both sides of the Atlantic, it is probable that most of the large-seeded river-side genera common to Europe and North America, such as Iris and Acorus, had in past ages their home in the extreme north, whence the plants spread as from a focus into the continents of America and Eurasia. It is also to be doubted whether even in the tropics there has been much over-sea dispersal of Limnanthemum without the aid of man, and reasons will be given for the belief that probably in Fiji, in the New Hebrides, and in New Caledonia the seeds of the first plants were unintentionally introduced by the aborigines.

Following Bentham we may regard the species of the Western Pacific Islands as a form of the wide-ranging Limnanthemum indicum. These plants in Fiji do not play the part in river-vegetation that they do in the temperate regions, as for instance in the Upper Thames. They are not common except in places, and seem to be chiefly confined to Viti Levu, particularly to ponds in the Rewa delta, where their rôle is that of an Indian tank plant. In the Rewa delta they may be sometimes seen thriving in brackish water having a density of 1·005.

Looking at the mode of dispersal to which the Limnanthemums owe their existence in the Western Pacific, we cannot disregard, especially in Fiji, the possibility of the seeds having been unintentionally transported by the natives when they carried in their migrations their edible tubers, such as Colocasia antiquorum, Alocasia indica, and Cyrtosperma edulis, that are cultivated in wet places. It is in the ponds around which these plants grow that the Limnanthemums thrive. The Chinese, with their peculiar methods of cultivation, are now carrying with them strange water-plants over the warmer regions of the globe; and it would be surprising if the Pacific islanders in their migrations did not do the same. If such an introduction, however, took place, it must have happened before the time of Captain Cook, when the plant was found in New Caledonia. (It may be remarked in this connection that the seeds of the genus will germinate after being kept dry for years. Seeds of the British species which I had kept dry for two and a half years germinated healthily when placed in water.)

Some years ago I ascertained that the seeds of the British plants were enabled, by means of their fringe of hairs, to attach themselves firmly to the downy plumage of a bird’s breast. This could not happen with the Fijian plant as the seeds are naked, and the same may be said of some species described by Gray and Chapman as widely spread over the United States. The seeds of the genus appear quite unsuited for safe transport inside the body of a bird. The Fijians give the plants a variety of names, nearly all of which are associated with the word for a duck, and none of them bear an ancient impress. Thus we find such names as “Ndambe-ndambe-ni-nga” and “Vothe-vothe-ni-nga,” meaning respectively “the duck’s seat” and “the duck’s paddle.”

Ceratophyllum demersum

This wonderful aquatic has been dispersed over most of the globe; but I will only mention its occurrence in oceanic islands, such as Fiji, Samoa, the Bermudas, and the Azores, to indicate the necessity of attributing its distribution in islands to birds. Several years ago I made a careful study in England of the habits and mode of germination of this plant, the results of which are given in Science Gossip for November, 1894; but reference can only be made here to such points as bear on the occurrence of the plant in the Pacific islands.

It is well known that in our English ponds and rivers the plant propagates itself, as a rule, by budding; and that it is only in unusually hot and dry summers, such as that of 1893, when many ponds became very low and were excessively heated, that the fruits mature in any quantity. My observations clearly showed that a higher temperature is required for the completion of maturation than for the early stage of the fruiting process and for the flowering. After a comparison of my river and pond temperatures, I formed the conclusion that whilst in water 12 to 18 inches deep this plant requires for a week or more an average daily maximum water temperature of 70° F. to produce its flowers, a warmth of 80° and over is necessary to mature its fruit, a condition to be found in England only in shallow ponds, where the plants may fruit abundantly, but not in rivers, where they flower and rarely mature the fruit (see also for the thermometric conditions my paper in Proc. Roy. Phys. Soc. Edin., xii, 296). Since a yet lower temperature (an average maximum water temperature of 66° for a week or more) is sufficient for germination, it follows that the thermal conditions of our English climate will allow Ceratophyllum to germinate and to flower, though but rarely to mature the fruit.

Even in Fiji we can notice the distinction between the cooler river and the superheated ponds and swamps of the Rewa delta as regards the maturation of the fruit. In 1897 I found Ceratophyllum thriving in the main channel of the Lower Rewa where the water was quite fresh; whilst lower down where the water was often brackish its place was taken by Ruppia maritima. In the main river, where the water unmixed with sea-water rarely acquires a temperature of 80° F., the reading being usually 78° to 79°, I never found the plants in fruit, and it is only in the superheated shallow waters of the swamps and back-waters that they mature their fruits.

Since Ceratophyllum even in tropical climates would probably only mature its fruits in the superheated waters of shallow ponds, tanks, and ditches, it follows that its dispersal by birds is confined to warm regions. In the cold waters of the Siberian lakes and rivers it would never mature its seeds, and could only be propagated by budding. If it existed in the head-springs of the sources of a river in these latitudes, it would be distributed by means of its floating shoots and fragments along the length of the river basin, and in the times of flood it might pass in the lower plains from one river system to another. When rivers changed their courses it would be left behind in the lakes and ponds and springs, and would also be carried away to the new region. In this manner it would in the course of ages be distributed over a continent without the aid of seed, propagating itself in a vegetative fashion.

In the case of oceanic islands, however, we have to appeal to the seed. Since the fruits sink in sea-water even after prolonged drying, and since a few days’ immersion in sea-water, as I found, kills the floating plant, we are driven to the agency of birds. The fruits, which without appendages are a quarter of an inch (6 mm.) in length, are too large and heavy to be carried in dry mud adhering to birds. The chances of their becoming entangled in a bird’s feathers by means of their basal spines and terminal style seem small, since they would be lying usually on the mud under the water. They are quite fitted for safe transport in the stomach and intestines of birds, such as is established in Chapter XXXIII for Potamogeton and Sparganium in the case of ducks. As my experiments show, drying for a period of three months does not injure the germinating capacity of the seeds.

Dracontomelon (Anacardiaceæ)

This is a genus accredited in the Index Kewensis with eight species, of which three belong to Borneo, one to Sumatra, one to Java, one to the Philippines, and two to Fiji, all the species being restricted in their range. My observations were confined to D. vitiense, Engler (D. sylvestre in Seemann’s work), the Tarawau of the Fijians, who regard it as a tree that is planted by the dead in Naithombothombo, the place of departed spirits, according to the legend given by Hazlewood in his Fijian Dictionary. Its method of dissemination in the Fijian forests is, however, far more prosaic. Pigs and fruit-pigeons assist in the dispersal of the seeds in these islands. Pigs are often found in the vicinity of a Tarawau tree; and evidently they much appreciate the fallen fleshy fruits, which are about 1-1/3 inch (3·3 cm.) across and inclose a large stone 7/8 inch (2·2 cm.) in diameter. The entire fruit and the detached stone sink in sea-water, the last floating only a few hours, even after drying for four years. Mr. Hemsley regards the genus as probably dispersed by the currents, since a stone was found amongst the floating drift collected by the Challenger Expedition off the coast of New Guinea. The stone, however, is described as seedless, which may explain its buoyancy. It is, however, to the fruit-pigeon that we must look for the dispersal of this genus. In the crop of one of these birds shot in Fiji I found the entire fruit of a Tarawau tree.

Canarium (Burseraceæ)

This genus of trees, to which nearly a hundred species are referred in the Index Kewensis, belongs mainly to tropical Asia and Malaya, a few species occurring in tropical Africa, Madagascar, the Mascarene Islands, and Polynesia. Its great home is in Malaya, to which two-thirds of the species are confined; but its distribution in the oceanic islands of the Indian and Pacific Oceans is especially interesting, Mauritius, Bourbon, Fiji, Tonga, and Samoa (Horne) each possessing a species.

The large drupes of the genus, as I found in Fiji, have no capacity for dispersal by currents; and we are, therefore, compelled to appeal to the agency of the frugivorous bird. Yet to a person unaccustomed to the ways of fruit-pigeons the transportation across a broad tract of ocean of large heavy “stones,” an inch and more in size, would seem impossible; and even to a student of dispersal improbable. Unless, however, we prefer to accept the Lemurian theory for the Indian Ocean and the theory of a Melanesian continent for the Pacific we are compelled to appeal to these birds; and it can scarcely be said that our appeal is without some justification. Both in the Solomon Islands and in the Fijis I was familiar with the dispersal of the stones of these trees by fruit-pigeons; and Wallace, amongst other writers, observed the same long ago in the Malayan Islands (Malay Archipelago). Stones obtained from the crops of Fijian pigeons measured 1-2/10 × 1 inch (3 × 2·5 cm.). In the Solomon Islands these birds stock the interior of the coral islets with trees of the genus, and the ground below the trees is often strewn with the disgorged stones (Bot. Chall. Exped., iv, 310; Guppy’s Solomon Islands, p. 85).

Although the difficulty concerned with the transport of the seeds across a broad tract of ocean seems very great, it is quite possible that further investigation will enable us to overcome this objection, just as we have done in Chapter XXVI when explaining how the genus Elæocarpus may have reached Hawaii. It is, indeed, not unlikely that, as with Elæocarpus, the stones of the drupes may in some species be much smaller and far more fitted for being carried in a bird’s body over several hundred miles of ocean.

Couthovia (Loganiaceæ)

Reference is here made to this genus because its mode of dispersal is known, and because I was familiar with it in Fiji. Seemann gives two species for Fiji, C. corynocarpa and C. seemanni, and the few other species known seem to be confined to the Western Pacific. Solereder gives a third species, C. densiflora, for Kaiser-Wilhelmsland in New Guinea (Engler’s Pflanz. Fam. teil 4, abth. 2); and a Solomon Island species, nearly allied to, if not a variety of, the Fijian species, C. seemanni, is referred to in the list of plants from that group given in my book on those islands. I found C. corynocarpa not infrequently growing on the banks of small rivers in the heart of Vanua Levu. Its drupes, which float for a few days in sea-water, are, according to Seemann, eaten by fruit-pigeons. The “stone” varies from 2 to 4 centimetres (3/4 - 1-1/2 inch) in length; and from the standpoint of dispersal the genus ranks with Canarium and Dracontomelon. Seemann describes and figures this species, which was constituted by Gray, in his Flora Vitiensis; but, apparently through an error, it is in the Index Kewensis accredited to Hawaii. Hillebrand makes no reference to the genus in his book on the Hawaiian flora.

Veitchia (Palmaceæ)

This genus of palms is closely allied to Ptychosperma, a Malayan genus also represented in Fiji. The Index Kewensis names four species, one New Hebridean, and three Fijian. The fruits of two of the last-named species tested by me had no floating power. The seed is about an inch long, and the genus would be likely to be spread by fruit-pigeons. From the standpoint of dispersal the genus would be placed with Canarium and Couthovia; but possibly its presence in the Pacific may be indicative of an ancient Western Pacific continent.

Hibbertia (Dilleniaceæ)

This genus of some eighty known species is almost entirely Australian, with the exception of a few species found in New Caledonia, Tasmania, and apparently also in the Mascarene Islands. Horne was the first to record a species from Fiji, where it grows commonly in the “talasinga” plains on the lee sides of the islands, and also on the scantily vegetated mountain summits. In Vanua Levu I often found these plants growing on the rocky peaks of the highest mountains of the island, as on Mbatini, 3,500 feet, and on Mariko, 2,900 feet. Their presence on these isolated peaks can only be attributed to birds. The carpels contain one or two seeds, which have a membranous aril; but in the plains the seeds are usually destroyed by grubs.

Myrmecodia and Hydnophytum (Rubiaceæ)

These two genera of epiphytes, distributed over Malaya and extending to the islands of the Western Pacific, possess tuber-like stems, which are extensively chambered by ants that find a home in the interior. They were familiar to me in the Solomon Islands, where they frequently grow on the mangroves and on other littoral trees. They do not form such a feature in the shore vegetation of Fiji, and judging from the observations of Dr. Seemann and myself they occur most often on the wooded mountain-peaks. The berries of these plants would attract frugivorous birds; and their pyrenes, which in a Fijian Myrmecodia I found to be 4 millimetres long, appear quite suitable for dispersal through this agency. It would seem that germination may occur in the berry on the plant. A specimen of Myrmecodia in fruit, that had been lying overlooked for a fortnight between newspapers during one of my mountain journeys, displayed on examination the pyrenes in a germinating condition, the process being subsequently completed. The reader will find these interesting plants described and illustrated in the English edition of Schimper’s work on Plant-Geography, pp. 149, 150.

Myristica

The Nutmeg trees, though principally at home in Indo-Malaya, are found also in the warm regions of Africa and America, as well as in the islands of the Western Pacific from the Solomon group eastward to Fiji, Tonga, and Samoa. The Tongan and Samoan groups possess two species in common, whilst Fiji seems to possess its own species, four or five in number.

The seeds of this genus have long been known to be dispersed by fruit-pigeons. Mr. Moseley, in his Notes of a Naturalist, and in the Journal of the Linnean Society (vol. xv), tells us how at one time these birds in their dissemination of the seeds in the Banda Islands were active opponents of the policy of the Dutch Government in preserving their monopoly of the cultivation of the nutmeg of commerce. He found numbers of wild nutmegs in the crops of these birds in the Admiralty Islands, some of which were partially digested and others seemingly sound; and Mr. Hemsley includes the genus as amongst those dispersed in the Western Pacific by birds (Bot. Chall. Exped., Introd. 46; iv, 229, 308). In my book on the Solomon Islands I refer to the occurrence of these seeds in the crops of fruit-pigeons; and I found that the seeds were similarly dispersed by these birds in Fiji. It is likely that the absence of the genus from Eastern Polynesia is to be partially connected with the insufficient protection of the seeds against injury during such a long ocean passage in a bird’s body.

Gaudichaud, as quoted by Hemsley, refers to the occurrence of the fruits of three or four species of Myristica in the drift floating in the Molucca Sea. When in the Solomon Islands I noticed that the unopened fruits of a species floated in sea-water. In later years in Fiji I tested this point, and found that whilst the fruits just before dehiscing will float between three and seven days in sea-water, the seeds sink. As I have pointed out in the chapter on Drift, rivers carry down to the sea an abundance of seeds and fruits that can float a few days but do not imply dispersal by currents.

Although, as I have above remarked, the localised range of the genus in Polynesia may be in part connected with the insufficient protection of the seed, it is apparent that in the case of a genus found in Asia, Africa, and America we are brought into contact with questions other than those of means of dispersal. No one would pretend that Myristica seeds could be carried by birds uninjured across the Pacific Ocean; and to explain the present distribution of the genus we must recall cases of a similar kind, such as Podocarpus, where the genus in past ages had a home in the north, from which, as from a focus of dispersion, it extended into the continents of the Old and the New World (see p. 302).

Rhaphidophora (Araceæ)

This genus of climbing aroids, which gives a character to the forests of Indo-Malaya as well as to those of the Western Pacific, is represented in the New Hebrides, Fiji, Tonga, and Rarotonga by a variety of the widely spread R. pertusa that ranges over Indo-Malaya and Eastern Australia. The ripe berries would readily attract birds; and the seeds, 4·5 millimetres long in the case of a Fijian plant, appear hard enough to pass unharmed through a bird’s digestive canal. We seem here to have evidence of a somewhat recent connection between Indo-Malaya and Polynesia through the agency of frugivorous birds. That the genus has been long established in Polynesia is, however, indicated by the occurrence there of a species seemingly peculiar to Fiji. We are disappointed that in Engler’s recent contribution to the Pflanzenreich (in his volume on the Araceæ-Pothoideæ) he has not been able to include this genus in the field of his studies.

Gnetum (Gnetaceæ)

This Gymnospermous genus, which is found in the warm regions both of the Old and the New World, is represented in Fiji by a Malayan species, Gnetum gnemon, which exists also in the Solomon group with other species of the genus (Guppy’s Solomon Islands, pp. 288, 301). I was familiar with this species in both Fiji and the Solomon group; but in the first-named locality it is seemingly restricted to the borders of Wainunu Bay on the south side of Vanua Levu, where Dr. Harvey first found it. It grows there abundantly in young wood.

It seems almost idle to discuss the mode of dispersal of a genus that is placed in a class apart with the African Welwitschia and the European Ephedra, possessing with them a history of which we know nothing. Yet it is ranked by Mr. Hemsley amongst those genera that are dispersed in Polynesia by birds, and he produces better evidence in support of this view than we possess for many other plants. Thus a fruit of a species of Gnetum, perhaps G. gnemon, has been found in a New Guinea fruit-pigeon; and the fruits of two species of the genus were found in the crops of fruit-pigeons shot by Mr. Moseley in the Admiralty Islands (Bot. Chall. Exped., Introd. 46; iv, 308). The red drupes of Gnetum gnemon of Fiji would readily attract birds, and their nut-like stones, about 8 millimetres long, are well suited for this mode of dispersal. My experiments in Fiji show that neither the drupe nor the stone of this species floats in sea-water; and it is probable that the fruits of this genus referred to by Mr. Hemsley as having been picked up on the beach in the Aru Islands possessed only a temporary buoyancy.

This genus presents us with the same puzzling question put to us by several Fijian genera, such as Myristica and Podocarpus, that occur in both Asia and America; and until we answer that query it seems almost futile to study modes of dispersal.

Elatostema (Urticaceæ)

This genus of annual and perennial herbs belongs to the tropical regions of the Old World. It is represented in Samoa by fifteen known species and by at least four or five in Fiji, whilst with the exception of a solitary Tahitian species it is not recorded from East Polynesia. Reference is here made to it particularly on account of its great development in Samoa. We have here a genus that, like Psychotria in Fiji and Cyrtandra in Fiji, Samoa, and Hawaii, runs riot in respect to the production of species (see p. 317). Dr. Reinecke describes fifteen Samoan species, of which, with the exception of two found in Malaya, all seem to be described for the first time. So sensitive, he remarks, is the genus to external conditions that station-forms abound; and he points out that if we were to follow the dividing lines usually recognised between species, we should account every station-form a new species. It is, of course, obvious that the polymorphism of the Samoan Elatostemas depends primarily not on the varying influence of station but on their sensitiveness to external conditions. One might put the question to the Samoan Elatostemas that Hillebrand put to the Hawaiian Cyrtandras, and ask why nature in this particular genus in this particular locality thus luxuriates in formative energy. Almost every Pacific group in respect of some of its plants presents the problem so well stated by Dr. Reinecke for this genus in Samoa. It is noteworthy that Schimper, in his work on Plant-Geography (English edition, pp. 291, 297, 299), especially singles out Elatostema and Cyrtandra as growing socially in the tropical rain-forests of Java and of the Asiatic mainland.

Scirpodendron costatum (Cyperaceæ)

As far as I can gather, this giant-sedge has not been previously recorded from Fiji; but it is included in the Samoan flora, and has also been found at Penang and Singapore, as well as in Borneo, Java, and Queensland. In Samoa, as we learn from Reinecke, it grows both in the coast swamps and on dry ground. In Fiji it is very common in the mangrove-swamps at the mouths of rivers, especially in the Lower Rewa; but in Vanua Levu it is also frequent in the marshy localities of inland plateaux, 700 to 800 feet above the sea, as well as by the side of streams in swampy districts on the lower hill slopes. This double station in the salt-water swamp of the coast and in the fresh-water marsh of the interior seems to be repeated in Java, where the plant was first discovered by Zippelius on the banks of torrents in mountainous regions and in swampy places.

The genus comprises, according to the Index Kewensis, only this species, though variations are to be observed in plants from different localities. The species was described by Kurz in the Journal of the Asiatic Society of Bengal (vol. 38, 1869) and by Bentham in his Flora Australiensis; and an illustration is given by Miquel in his Illustrations de la Flore de l’Archipel Indien (1871). The plant is so common in Fiji that one can only suppose that its resemblance to a stemless Pandanus, from which, as Kurz observes, it is with difficulty distinguished except when in flower or fruit, led to its being overlooked by both Seemann and Horne. Its leaves, from 9 to 12 feet in length, are commonly used for making mats and for thatching, both in Fiji and Samoa. The plant usually attains a height of 3 to 5 feet.

The fruits occur abundantly in the floating and stranded river and sea drift in Fiji, a circumstance that led to my discovery of the parent plant in the swamps. The fruit, which is about half an inch (12 mm.) long, consists of a hard, stony nut invested by a thick ribbed cork-like covering, to which it owes its buoyancy, since the nut sinks. The detached fruit is perforated at the base through both coverings, and only a little soft tissue closes the aperture in the inner shell, the protection against the entry of sea-water in the case of floating fruits being quite inadequate. This explains also why the stranded fruits were so frequently found by me germinating on the beach, where, as my observations showed, they never established the plant. This early germination would prove to be an advantage in the case of fruits stranded in a suitable locality.

But though the perforation in the fruit favours its early germination, it lessens its ability to withstand a long sea-passage without injury to the embryo. I found in different experiments on fruits of plants growing in the mangrove swamps, that when placed in sea-water 40 per cent. sank during the first fortnight, whilst 15 per cent. floated after five or six weeks, but all were at the bottom in two months. On the other hand, fruits from plants of the swamps of the inland plateaux displayed much feebler floating power, in some cases sinking at once, in others floating for a few days, and in others again floating for a week or two. In this case the outer cork-like covering proved to have lost most of its floating power.

From the number of empty seed-vessels found, both in the floating and stranded drift, it appeared evident that the seed had often rotted away during the flotation. It is apparent from these observations and experiments that Scirpodendron costatum is not suited for dispersal by currents over wide tracts of ocean. The fruits might be able to float unharmed for a few weeks, but they would be unable to accomplish much more than the 500 or 600 miles intervening between Fiji and the nearest groups to the west.

Lemnaceæ

This order, judging from the writings of Hegelmaier, Schenck, and Hemsley, is represented by one or other of the common species, Lemna minor, L. gibba, L. polyrrhiza, in various Atlantic islands, as in the Bermudas, the Azores, Madeira, the Canary Islands, and St. Helena; but doubts frequently arise as to their being truly indigenous. Lemna trisulca is regarded by Hemsley as indigenous in the Bermudas. Lemna minor has been introduced in recent years into Hawaii, where I observed it flowering and sometimes fruiting abundantly in the heated waters of the ponds. Two species found in other regions were recorded by Seemann from Fiji, and I have come upon few other records of the occurrence of the order in the tropical islands of the open Pacific. I am inclined to the opinion, based not only on the facts of distribution, but also on the results of numerous experiments on the means of dispersal, that this order has in most cases reached oceanic islands with man’s assistance.

Some years ago I made a systematic study of the habits of the British Lemnæ, most of the results being published in the Linnean Society’s Journal (vols. xxix and xxx), as far as concerned Lemna minor, L. gibba, and L. polyrrhiza. During this inquiry I ascertained that with these species, as well as with L. trisulca, the chances of a bird’s carrying their fronds uninjured in its plumage over a wide extent of ocean were small. None of them survived twenty-four hours’ drying in fine weather, whether in the sun or in the shade; but in rainy weather they withstand an exposure of one or two days. It is, therefore, unlikely, even if the fronds were entangled by their rootlets in a bird’s feathers, that they would be able under ordinary conditions to reproduce the plants after a day’s flight of some five hundred miles across the sea. It must also be remembered that the drying capacity of the air when a bird is in full flight in ordinary weather would be that displayed during a gale of wind with a velocity of at least thirty to forty miles an hour. For this reason I do not think with Kerner that under usual conditions drops of water would be a factor of importance in causing the adherence of minute seeds of any kind to birds’ plumage. Where the seeds are not available, it is most probable that birds disperse the duckweeds by their fronds over short distances, but not across broad seas. This would certainly apply to temperate latitudes, where these plants rarely seed. Thus with Lemna, as with Ceratophyllum, it would seem that the dispersal of the seeds by birds takes place normally only in warm latitudes. Those of the duckweeds could be transported in adherent mud over land-areas.

According to Hegelmaier, the two species of Lemna found in Fiji are L. paucicostata, an Asiatic species, and a variety of an Australian species, L. oligorrhiza, possessing dark root-sheaths. These plants mostly came under my notice in the Rewa delta. They were rarely seen in Vanua Levu, where in one locality I found the typical Lemna minor. The first species is also Samoan.

In 1897 and in 1899, in a pool near Notho in the Rewa delta, in Viti Levu, Fiji, I found a great abundance of a species of Wolffia, specimens of which were sent to Prof. Schimper with my mangrove collections, but his death intervened, and I have not been able to follow up the matter. On comparing the specimens with Hegelmaier’s descriptions and plates, it would seem that the species is near W. arrhiza and W. brasiliensis, but differs from both in the greater length of the fronds. As concerning the means of dispersal of the genus, I may add that the fronds were killed after being allowed to dry for eighteen hours.

Marsilea (Marsileaceæ)

A species of this genus, apparently near Marsilea villosa, was common in the ditches and ponds around Notho, in the Rewa delta, Fiji, in 1897-99. The genus is included by Horne in his list of Fijian plants; but is not given by Seemann. The villous sporocarps, when dry, are very light and readily catch in cloth and in feathers. Hillebrand includes in the Hawaiian flora M. villosa and M. crenulata. The first-named, which was collected by Chamisso and Gaudichaud, finds (he says on the authority of Braun) its nearest relative in a species from Oregon and California. The other has been collected in the Liukiu Islands, the Philippines, Mauritius, and Bourbon. It is very probable that the occurrence of the genus in oceanic islands is due to the agency of birds.

Summary of the Chapter

(1) We are here concerned with the more restricted distribution of non-endemic tropical genera over the Pacific. The general trend eastward of these genera is well brought out in the fact that whilst Fiji possesses some sixty or seventy genera in common with Tahiti to the exclusion of Hawaii, it does not possess a score in common with Hawaii to the exclusion of Tahiti. The grasses and sedges and the mountain genera are not here included; and we are comparing the flora of the Hawaiian lowlands below 4,000 feet with the floras in mass of Fiji and Tahiti.

(2) Hawaii possesses very few genera (less than thirty) that are not found either in Fiji or in Tahiti, or in both; and of these quite a third are to be traced to America.

(3) From two of these genera, Embelia, a land genus, and Naias, an aquatic genus, we obtain two important indications, namely, that specific differentiation has taken place to much the same extent in a water plant as in a land plant, whether in a continent or in an island. In other words, new species have been developed or are developing independently of the immediate environment and of isolating influences.

(4) The interchange of plants between the regions of Hawaii and Tahiti to the exclusion of Fiji has been very slight. Probably not half a dozen genera belong to this category.

(5) Excluding plants brought by man and by the currents, Tahiti possesses very few that present any difficulty from the standpoint of dispersal, plants with seeds or “stones” an inch in size being, as a rule, absent.

(6) With the genera (60-70) common to Fiji and Tahiti, and distributed, therefore, over the South Pacific, the wide-ranging highly variable plant is an important factor in the development of peculiar species in the different groups, just as it has been shown to be in the previous chapter in the case of genera dispersed over the whole Pacific. The rôle of the polymorphous species has always been an important one in this region.

(7) In the case of several Fijian genera it seems almost futile to talk of existing means of dispersal, since the present distribution of genera like Sterculia and Gnetum, that occur on both sides of the Pacific, in America and in Asia, is not to be thus explained.

(8) On account of the large size of their seeds and “stones” it might be argued that certain of the Fijian plants afford evidence of a previous continental condition of the islands of the Western Pacific, since it is not easy to understand how such large seeds and “stones” could have been transported over broad seas by birds. It is, however, pointed out that in these respects the species of a genus may vary greatly, and that the seeds and stones may be large in some species and small in others.

(9) The greater number of the genera that have entered the Pacific from the Old World have not advanced eastward of the Fijian region, half of the Fijian genera not occurring in the Hawaiian and Tahitian regions; and the explanation of this is to be found not in any lack of capacities for dispersal, but in a want of opportunities. The story of plant-distribution in the Pacific is bound up with the successive stages of decreasing activity in the dispersing agencies. The area of active dispersion that at first comprised the whole of the tropical Pacific was afterwards restricted to the South Pacific, and finally to the Western Pacific only. The birds that in an early age carried seeds all over this ocean became more and more restricted in their ranges, probably on account of increasing diversity of climatic conditions. The plants of necessity responded to the ever narrowing conditions of bird-life in this ocean, and the differentiation of the plant and of the bird have taken place together.

Spotted a typo or a problem in this chapter? Tell us

XXVIII. THE POLYNESIAN AND HIS PLANTS

Identity of the problems presented by the indigenous plants and the peoples of the Pacific islands.—The food-plants of the Polynesians and the pre-Polynesians.—Their weeds.—The aboriginal weeds.—The white man’s weeds.—Weeds follow the cultivator but are distributed by birds.—The general dispersion of weeds antedates the appearance of the Polynesian in the Pacific.—Weeds of little value to the ethnologist.—Aleurites moluccana.—Inocarpus edulis, Gyrocarpus Jacquini, Serianthes myriadenia, Leucæna Forsteri, Mussænda frondosa, Luffa insularum.—Summary.

MAN AND THE SEED

MAN in his distribution in the islands of the Pacific reproduces in a minor degree nearly all the difficulties presented there by plants, birds, and other forms of animal life. Like the plant he entered the ocean from the west; and as with the plants, so with the aborigines, there was an era of general dispersion over this ocean, followed by an age in which Polynesian man, ceasing to migrate, tended to settle down in the several groups, there undergoing differentiation in various respects, as in physical characters, in language, and in manners. Just as we can now recognise the type of a plant, of a bird, or of an insect, that belongs to a particular group of islands, so we can distinguish between the Hawaiian, the Tahitian, and the Maori, whether in physical characters, in his speech, or in his customs. Fiji possesses in the Papuan element of its Melanesian population the earliest type of man in the Pacific, just as it also possesses in the Coniferæ the most ancient types of trees in this region. Divesting his mind of all previous conceptions, the ethnologist, as I have remarked in my discussion of the distribution of Freycinetia in Chapter XXV, might profitably study de novo the dispersion of man in the Pacific from the standpoint of plant-dispersal.

Man and the seed have battled their way over the Pacific apparently in defiance of the prevailing winds and currents, and both have failed to reach the New World. Man in the Pacific is almost as enigmatical as the plant. As a denizen of this region he is by no means a recent introduction; and though his food-plants are mainly Asiatic, they belong to distinct ages in the history of man’s occupation of these islands.

I venture to think that a great deal lies behind the Indo-Malayan mask of the Polynesian, and that there is a story concerned with his origin that has yet to be told. We have by no means solved the riddle when by following the evidence we assign to him a home in Asia. It is only then that the real difficulties begin. It required many centuries of European civilisation for the discovery of America; but the voyages of Columbus sink into insignificance when we reflect on what had been dared and accomplished by uncivilised man when he first landed on the shores of Hawaii and Tahiti.

The problem of man in the Pacific bristles with difficulties differing in degree but not in kind from those relating to the flora. Whenever a particular theory seems on the point of being well established, some disturbing question arises, and as with the plant, we are never able to push our facts quite home. Since I first visited the Solomon Islands, now twenty-four years ago, the Pacific islander and his flora have deeply interested me. The history of man and of the plant cannot be separated in the Pacific; and the same determining principles of distribution have affected both.

THE FOOD-PLANTS OF THE POLYNESIANS AND PRE-POLYNESIANS

One can imperfectly distinguish two sets of food-plants in this region; the first comprising such plants as Pachyrrhizus trilobus, Tacca pinnatifida, Amorphophallus campanulatus, the Mountain Bananas, the Wild Yams, and several others that grow wild, and, as a rule, only serve as food in times of scarcity; the second including the plants that are extensively cultivated by the present islanders, such as the Breadfruit, the Banana (Musa paradisiaca), the Taro (Colocasia antiquorum) and the two Yams (Dioscorea alata and D. sativa), &c. Those of the first set probably formed the food of the earliest inhabitants of the Pacific Islands, pre-Polynesian peoples that practised only a rude sort of cultivation, as with the present “bush-men” of the islands of the Western Pacific. Those of the second set belong to the later occupants of these islands, the Polynesians.

(a) The Pre-Polynesian food-plants.—In addition to those above named one may mention Cycas circinalis, Cyrtosperma edulis, Lablab vulgaris, Pandanus odoratissimus, Saccharum officinarum, Sagus vitiensis, &c. Inocarpus edulis is probably to be here included, and amongst the Wild Yams should be named Dioscorea nummularia and D. pentaphylla. Some of them are now occasionally cultivated; but most of them only occur in the wild condition, either as weeds or as larger plants growing spontaneously in uncultivated localities. Even the knowledge of them as food-plants has sometimes been altogether lost, the present inhabitants of the Fijis, for instance, knowing nothing of Lablab vulgaris and Sagus vitiensis as sources of food. The question of the antiquity of the Coco-nut Palm in Polynesia was discussed at length by Seemann; but for various reasons we cannot be absolutely certain whether or not it is an older denizen of the Pacific islands than the Polynesian. It is, however, to be inferred that it came originally from the home of the genus in America, perhaps as a gift brought by the Equatorial Current from the New World to Asia. Several chapters might be devoted to the discussion of the earlier food-plants of these islanders; but here only a brief reference can be made to a few of them.

Perhaps the oldest of the earliest aboriginal food-plants are those that, like Cyrtosperma edulis and Sagus vitiensis, are apparently confined to Fiji. Here we seem to possess indications of the development of new species since that group was first occupied by man. Others, like Pachyrrhizus trilobus and Cycas circinalis, that are restricted to the groups of the Western Pacific may come next in relative antiquity.

Although most of the early food-plants hail from the Old World, the home of Pachyrrhizus is in America. One may indeed wonder how a plant with such a history ever reached the Western Pacific. It seems to be generally distributed in this part of the ocean, having been recorded from New Caledonia, the New Hebrides, Fiji, Tonga, and Samoa. Although its edible roots are only used in times of scarcity, the plant grows wild all over Fiji, being especially frequent in the “talasinga” plains. Though I searched diligently, it never presented me with its seed. In Tonga, according to Graeffe (as quoted by Reinecke) the plant is much employed in preparing the land for yam-cultivation, since it restrains the growth of weeds and keeps the soil moist.

Amongst the food-plants of this early period that are distributed over the South Pacific as far east as Tahiti may be mentioned the Wild Yams (D. nummularia and D. pentaphylla), the Mountain Bananas, Tacca pinnatifida, Amorphophallus campanulatus, and others. Of these Tacca pinnatifida and Dioscorea pentaphylla are alone found in Hawaii. I will only now refer to the Mountain Bananas.

The Mountain Bananas of the tropical South Pacific, distinguished by their erect fruit bunches and their seeded fruits, present us with one of the mysteries connected with aboriginal man in this ocean. Whether in New Caledonia, Fiji, Samoa, Rarotonga, or in Tahiti, they grow wild in the interior, and form often a conspicuous feature of the vegetation in the mountains and at the heads of the valleys. They are occasionally cultivated. Their Fijian and Samoan names of “Soanga” and “Soa’a” reproduce the names of the banana, “Saguing” and “Saing” in the Tagalog language of the Philippine Islands. The Tahitian appellation is “Fehi” or “Fei,” and this reappears in Samoa in the form of “Fa’i,” the word for the common cultivated banana, Musa paradisiaca. The Rarotongan name of “Uatu,” as given by Cheeseman, is suggestive of the Micronesian form (Ut, Uut, &c., in the Carolines) of a widely spread banana word in Malaya, Melanesia, and West Polynesia (Fudi, Vundi, Undi, &c., &c.). It is not unlikely that all these South Pacific mountain bananas with erect inflorescences and seeded fruits belong to one species, variously designated by botanists as Musa fehi, M. uranoscopus, M. troglodytarum, &c., and confined to this region. Under the name of Musa fehi Schumann includes the New Caledonian and Tahitian plants, and he views the Samoan plant as probably identical with them. This botanist, in his monograph on the Musaceæ (Engler’s Das Pflanzenreich, 1900), establishes the home of the bananas in tropical Asia, and considers that their occurrence in America before the time of Columbus has not been proved. Birds have no doubt often assisted in the dispersal of the wild, seeded plants; but it is likely that man is responsible for the occurrence of the mountain forms in the Pacific, and probably their fruits formed when cooked one of the principal articles of diet of the earliest immigrants. (There evidently exists in Vanua Levu a plant very like the African Musa Ensete. Its presence was only indicated by the occurrence of its empty seeds in the stranded beach-drift, and reference is made to it in that connection in Chapter XXIX.)

(b) The Polynesian food-plants.—The cultivation of the yams, the taros, the breadfruits, and the bananas in later ages all over the Pacific islands cannot here be dealt with. My readers will already know that a very ancient cultivation is in each case indicated by the occurrence of a great number of varieties. Much has been written upon this matter, and amongst the recent contributions to the subject may be reckoned Mr. Cheeseman’s interesting paper published in the Transactions and Proceedings of the New Zealand Institute (vol. xxxiii).

I may here mention in connection with the Sweet Potato (Batatas edulis), a plant that may have an American origin, though much mystery surrounds its home, that it rarely seeds in Fiji except when it is grown in poor, sandy soil, and in dry, rocky situations. The Fijians were quite incredulous as to its maturing seed; but after much searching I found a solitary plant in seed and removed their doubts.

THE POLYNESIAN WEEDS

Some curious questions are raised in connection with the weeds of this region. Polynesia, says Dr. Seemann, presents a most interesting problem with regard to its weeds. It is, however, necessary to point out that these plants arrange themselves into two groups, the aboriginal weeds comprising those existing in the islands at the time of Captain Cook’s expeditions in the latter half of the eighteenth century, and the white man’s weeds that have been since introduced.

As concerning the Fijian Islands, Dr. Seemann remarked that although the majority of the non-endemic plants of the flora is Asiatic, “the bulk of the weeds is of American origin, or, at all events, is now found in America.” His principal point was to show that American weeds displayed a greater disposition than Asiatic weeds to spread in Fiji, because Fiji was to American plants altogether virgin ground. This is a purely botanical matter, and we are not in a position to oppose a conclusion formed by such a careful observer of plant life. But to the ethnologist it is a very different matter whether most of the Fijian weeds are of American origin or merely now exist in America. His interest lies entirely in the aboriginal weeds. To the student of plant-dispersal this distinction is also a very important one; and his interest again is all on the side of the aboriginal weeds.

Dr. Seemann enumerates 64 Fijian weeds, of which at least 37 were in the Pacific islands when Captain Cook’s botanists made their collections (see Note 82). Of these 22 occur in continental regions on both sides of the Pacific, 13 are natives of the Old World alone, and two only are seemingly American exclusively, namely, Waltheria americana and Teucrium inflatum. The first is claimed to be American because most species of the genus are American, but it is now widely distributed in the Old World as well as in America. The second, though widely distributed in tropical America, has strangely enough only been found in the islands of the Western Pacific.

The important point is thus brought out that although in Captain Cook’s time the food-plants cultivated by the Polynesians, such as the banana, the breadfruit, the taro, and the yams, were almost exclusively Asiatic in origin and bore Malayan names, a large proportion of the weeds were not exclusively Asiatic, but occurred in America as well as in the Old World. The inference to be drawn, however, is not, as Dr. Seemann implies, that the Polynesians derived several of their weeds from America (since with few exceptions all the aboriginal weeds named in Note 82 occur in the Old World, and in more than a third of the plants in the Old World only), but that many so-called cosmopolitan weeds were distributed very much as they are now, when the Polynesians brought their food plants from Indo-Malaya into the Pacific.

Weeds follow the cultivator in all climates; and it is very natural that, as Mr. Hemsley points out, plants which seem to owe their wide dispersal to cultivation are not found in Australia (Bot. Chall. Exped., iii, 142). The Australian native as a rule cultivates nothing. Yet I fancy that man’s share in weed dispersal is as often as not merely restricted to producing the conditions favourable to the growth of weeds, and that the seeds are often brought by birds and other agencies. Many weeds of the genera Atriplex, Polygonum, and Ranunculus are dispersed by partridges in England, and I have often found the uninjured fruits of the plants in the stomachs of these birds. Many weeds, like Prunella vulgaris, Plantago major, Capsella bursa-pastoris, Luzula campestris, and several others named in Note 43, possess seeds or fruits that become “sticky” when wet, and would readily adhere to a bird’s plumage.

We can also say of tropical weeds that many of them are distributed by birds. In the crop of a dove in Hawaii I found a number of the small dry fruits of Waltheria americana, the widely spread tropical weed before mentioned, and of another weed of the order Compositæ. On the bare rocky peak of one of the Vanua Levu mountains the only plants found growing were Oxalis corniculata and a species of Peperomia, both of them evidently growing from seed dropped by birds. The fruits of Urena lobata and of species of Sida, as well as those of Bidens pilosa and Ageratum conyzoides, could be readily dispersed, entangled by their appendages in the plumage of birds, whilst the sticky achenes of Adenostemma viscosum would easily adhere to feathers. Weeds with drupes or berries like Geophila reniformis and Solanum oleraceum would attract frugivorous birds, and I have often seen berries of the last-named pecked by birds. Man has doubtless often been the agent in dispersing the seeds of Leguminous weeds like Lablab vulgaris. On the other hand, we know from the observations of Focke (see page 150) that birds can distribute the seeds of a plant like Vicia faba; and in the Pacific islands it is evident from the frequent occurrence of Tephrosia piscatoria on bare rocky hill tops that its seeds are dispersed through the same agency. Birds also probably carry about the seeds of Cardiospermum halicacabum.

If we based our conclusion solely on the distribution of weeds without a previous study of their means of dispersal we might, as students of the distribution of man, acquire some startling and very erroneous notions on the history of the races of man, especially in the New World. Lacking such an acquaintance with existing modes of dispersal it would not be prudent to attach too much importance to the occurrence of Asiatic weeds in America and of American weeds in Asia. Mr. Hemsley, in his work on the botany of Central America (Biologia Centrali-Americana), gives a list of ten British plants of world-wide range, which we will designate plants of waste places rather than weeds. They are plants often found not only in the Old and New Worlds, but also in the southern hemisphere, and I will here name them: Radiola millegrana, Alchemilla vulgaris, Cotyledon umbilicus, Lythrum salicaria, Convolvulus sepium, Sibthorpia europæa, Prunella vulgaris, Lycopus europæus, Aira cæspitosa, Luzula campestris. According to this authority these plants “are most unlikely to have been aided, intentionally or unintentionally, by man” and “possess no special means of dispersion by animals or birds or the elements” in the way, as is implied, of appendages like hooks, hairs, a pappus, &c.

Five of these plants are referred to in various connections already in this work. In all I have tested the means of dispersal of six or seven of them; and although my results are not always conclusive, I venture here to indicate some of them. The nutlets of Prunella vulgaris and the seeds of Luzula campestris emit mucus when wetted and adhere firmly to feathers on drying, whilst the nutlets of Lycopus europæus are sticky in the dry state and adhere to the fingers on handling. This last-named plant is occasionally to be noticed on rubbish heaps growing with other waste-plants. No such adhesive qualities, whether in the wet or dry condition, came under my notice with Alchemilla arvensis or with Lythrum salicaria. With Alchemilla the seed-like fruits fall from the plant, inclosed in the dried-up calyx. The seeds of Cotyledon umbilicus are so minute (1/3 mm. or 1/75 inch) that they can be compared with Juncus seeds from the standpoint of dispersal. They are naturally a little sticky and tend to adhere to feathers, but more probably they are transported in adherent soil. The case of Convolvulus sepium is a very remarkable one, and I have referred to it on page 29 and in the notes there indicated. The species of Radiola, Sibthorpia, and Aira have not been tested by me. Dispersion, however, would be favoured by the small size of the seeds in the first two species and by the awned glumes in the case of Aira.

The distribution of aboriginal weeds might be expected by some to supply data of profound interest to the student of the races of mankind; and I think the botanist rarely realises how often he tantalises the ethnologist by the remark that certain weeds have been spread by cultivation all round the tropics. De Candolle many years ago, in his Géographie Botanique, gave a list of nearly 100 plants, made up of Old World species naturalised in America and of American species naturalised in the Old World, and quite half of them were classed as plants distributed in one way or another through man’s agency. Now this is either a subject of supreme importance or it is of no interest to the student of man’s history. If it should prove that birds have done most of this dispersal, then the story of the aboriginal weed would be of little interest in connection with the races of man in the New World.

I will now refer briefly from the standpoint of dispersal to a few interesting Polynesian plants in which man has been in most cases more or less concerned in their distribution.

ALEURITES MOLUCCANA (THE CANDLE-NUT TREE)

Much interest is attached to this tree, which is found in India, Malaya, and North-east Australia, and occurs all over the Pacific, extending north to Hawaii, south to the Kermadec Islands, and east to Tahiti and Pitcairn Island (Maiden). In the Hawaiian Islands it is often so frequent as to form whole forests, or at all events to give a character to the forest zone up to 2,000 feet above the sea. Its prevalence in Hawaii might be regarded as evidence of its indigenous character; but its predominance there is due to the circumstance that it is one of the few forest-trees that the cattle and other animals avoid, most other trees falling victim to their depredations by the loss of the bark. In Fiji, though frequent in places, it does not form such a conspicuous feature in the vegetation as in Hawaii. In Samoa it is abundant in the coast-bush. In Rarotonga it forms with Hibiscus tiliaceus, as we learn from Cheeseman, the major portion of the lower forests, a circumstance which seems to indicate, since both these trees were probably introduced by the natives, that this island like Hawaii has lost or is losing many of its original forest-trees. In Tahiti, according to Nadeaud, it is common from the sea-level up to 3,000 feet above the sea.

As a Polynesian tree, Aleurites moluccana presents itself to me as an intruder which has often taken the place of trees of the primeval forests of these islands. That the natives usually employ the oily seeds for illuminating purposes is well known; and its prevailing name of Tuitui (Kukui in Hawaii) is derived from the Polynesian custom of threading the seeds before using them for lighting purposes. One of the Fijian names, “Sikethi,” is suggestive of “Saketa,” a name for the tree in the Ternate dialect of the Indian Archipelago. To the modes of dispersal of this tree, I have devoted much attention.

The more or less empty seeds of this tree are to be commonly found floating in rivers and stranded on beaches. I have found them in numbers on the beaches of Fiji and Hawaii in the Pacific, and of the south coast of Java and of Keeling Atoll in the Indian Ocean. In all I have examined many hundreds of these seeds, whether stranded on the beaches in the localities above named, or floating in the Fijian rivers and at sea amongst the islands of that archipelago. The seeds were always either empty or contained a kernel in an advanced stage of decay. A sound seed has no floating power under any condition; and sound seeds are only to be found in beach drift near the mouths of estuaries, where they have been freed by the decay of the fruits brought down by the rivers. During some dredging operations in the harbour at Honolulu several years ago, quantities of old Aleurites fruits and seeds were brought up. It is only by means of the floating fruit that the sound seed can be carried any distance by the currents; but even in this case the opportunities of wide dispersal are very limited. If one places in sea-water a number of well-dried fruits, most of them will sink within a week, and all will be at the bottom in a fortnight.

The seeds stranded on a beach are often found cracked. This I think arises from long exposure to the scorching rays of the sun. On account of the hardness of the shell it is very difficult to obtain the kernel entire; but the Mangaians get over this difficulty, as we learn from the Rev. Wyatt Gill, by slightly baking the seeds; whilst the Fijians, according to Mr. Horne, effect the same object by throwing the heated seeds into cold water. On one occasion I placed an empty seed on a tin plate kept at a temperature 115° to 120° F., a temperature near that which the seed would acquire when lying exposed to the sun on a tropical beach. After five days I found it had reproduced the cracks noticed in another empty seed from the Keeling beach.

Facts are not wanting with regard to the dispersal of the seeds by birds; but since the kernel alone is sought for by birds, and as there is no means of cracking the shell in their stomachs, such an agency is only available for local distribution. The Messrs. Layard inform us that in New Caledonia a small crow (Physocorax moneduloides) and a parrot (Nymphicus cornutus) are very partial to these seeds (Ibis, 1882). They were told that the crow cracked them by carrying them to a considerable height and letting them fall on a stone. We are not told how the parrot cracks the seed, which has a shell so hard that the Malays, I may remark, term the seed “bua kras,” or “the hard seed,” whilst a hammer is required to break it. However, since Indian parrots, according to Mr. J. Scott, are able to split open with their beaks the hard beans of Adenanthera pavonina (More Letters of Charles Darwin, ii, 349), they evidently possess ingenuity in seed-cracking.

My general conclusion with reference to this tree in Polynesia is that it could not have been distributed, except locally, by birds and currents; and that it owes its dispersion there principally to man. A contrary indication seems to be offered by the occurrence of the tree in the uninhabited Kermadec group; but since Cordyline terminalis also exists there, a cultivated plant widely dispersed by the Polynesians, it would appear that these islanders have formerly visited the group. It is also contended by Canon Walsh that the Cordyline of the Maoris was introduced into New Zealand by that race. (See Cheeseman in vols. xx and xxxiii, Trans. N.Z. Inst., for papers on the Kermadec flora and on the food-plants of the Polynesians.)

INOCARPUS EDULIS (THE TAHITIAN CHESTNUT)

Like Aleurites moluccana this tree presents a primâ facie case for dispersal by currents. As the result of inquiries in this direction I have formed the opinion, however, that it has been mainly distributed by man. Though occurring in all the South Pacific groups, as far east as Tahiti and the Marquesas, it does not occur in Hawaii. With its home in Malaya it possesses a range closely resembling that of the breadfruit tree; and yet, although its fruits are often a common article of food in Polynesia, it requires no cultivation, and reproduces itself so abundantly in favourable situations that, as Dr. Seemann observes, only the dense shade of the parents checks the occupation by the seedlings of all the adjacent ground. It possesses in the Pacific two sets of names, neither of which I have been able to identify with any Malayan names, and both occur over much of the region. Thus the Fijian “Ivi” and the Samoan and Tongan “Ifi” are represented by “Ii” in Rarotonga, “Ihi” in Tahiti and the Marquesas, “Hi” in Ualan in the Carolines, “Ifi” in Futuna in the New Hebrides, and “If” in a New Guinea dialect. Then we have the Tahitian “Mape,” the “Marap” of Ponape in the Carolines, and the “Mamape” of Fate in the New Hebrides, besides other forms found in Melanesia.

In the South Pacific islands, as in Fiji, Samoa, Rarotonga, and in the Tahitian group, it flourishes in low, moist localities at and near the coast, by the side of streams and estuaries, and in the rich soil of the lower valleys. In the Rewa delta in Fiji it is especially abundant, often bordering the creeks in the mangrove swamps, and occupying stations that are under water when the river is in flood. It may extend inland in the various groups, but it is in the low-lying, moist, coast regions that it mostly thrives; and in Fiji it presented itself to me as essentially a tree of the estuaries, a station strongly suggestive of dispersal by currents. Schimper, it may be remarked, includes it amongst the shore vegetation of the Indian Archipelago.

When in Fiji I paid especial attention to the dispersal by currents of these large fruits, the agency of birds being, of course, negatived by their size. They are to be commonly observed floating in the rivers when in flood, as well as at sea between the islands, and stranded on the beaches. Of those found afloat in the Rewa River not more than a fourth had a sound seed. Of those stranded on the beaches two-fifths were empty, two-fifths displayed a rotten seed, and one-fifth had sound seeds. Of those picked up at sea all were empty. These fruits, unlike many others in the drift of the Fijian rivers, do not germinate afloat. They soon lose in the water their outer, fleshy, non-buoyant coat; whilst the inner fibrous coat, to which the floating power of the fruit is due, the seed having no buoyancy, is not water-tight, and moisture soon enters and leads to the decay of the seed. In order to test their floating power, I placed in sea-water ten mature fruits. Five of them floated after forty-five days, having then lost most of the outer, fleshy coat. Two were afloat after sixty days, but their seeds were rotting. One fruit that sank after five weeks had a sound seed. Most of them were sown out afterwards in a place where the trees were thriving, but none germinated, and of two or three examined all had a decaying seed. The empty fruits may float a long time after the decay of the seed. Forty days would probably be the extreme limit for the flotation in sea-water of a fruit with a seemingly sound seed, though a very small proportion would reach this limit, and I much doubt whether such a fruit would germinate afterwards.

I, therefore, inferred that currents are only available for the local dispersion of the fruits of Inocarpus edulis. It is to man that the tree owes its existence in Tahiti and other groups of the open Pacific; and it is to be concluded that the occurrence of this tree on Christmas Island in the Indian Ocean marks an early Malayan occupation of the island.

GYROCARPUS JACQUINI

The cosmopolitan distribution of this seemingly useless tree, growing, as Hemsley remarks, in maritime districts throughout the tropics, in America, Australia, Asia, and Africa, presents one of the puzzles of plant-distribution. It is by no means universally spread in the Pacific islands, and I find reference to it only in Fiji and Tahiti. Seemann says that in Fiji it is common on the beaches of Taviuni and other islands. I found it to be a rare coast tree on Vanua Levu. It does not seem to have been recorded by the botanists of the 18th century in the Pacific. It, however, has evidently been long established there. Nadeaud does not speak of its littoral station in Tahiti, and says that it grows best in the regions of the interior up to elevations of 2,000 feet, where it attains a great size; and its abundance is implied by his remark that he had to fell many trees to collect the fruits.

The singular fruit, which has two long wings and looks like a shuttlecock, dries up on the tree; and in course of time it is detached and falls to the ground. The falling fruit in its descent twists round like a screw, and hence the Fijians call the tree the Wiri-Wiri tree, the same name in the form of Wili-Wili being given for a similar reason to Erythrina monosperma in Hawaii. Schimper (p. 157) truly remarks that the fruits are too heavy to be carried by the wind across a wide extent of sea; and I ascertained by experiment that in an ordinary trade-breeze they would only be carried a few paces. Birds are quite out of the question as agents of their transport to oceanic islands. We are driven then either to the agency of man or to that of the current. The trees grow rapidly and the timber is soft and perishable. The fruits are not edible, and as far as I could ascertain the tree is of little or no value to the Pacific Islander, there being at all events no reason to believe that he has distributed it.

We appeal lastly to the currents, the agency which Mr. Bentham selected on a priori grounds (Presidential address, Linnean Society, 1869). My experiments in Fiji showed that the fruits, when dried on the tree and afterwards detached, are able to float over long distances in sea-water. After two months they were still afloat, the seeds inside being dry and unharmed. The fruit’s buoyancy was tested in different conditions, either without the wings, or with both wings, or with but one wing, and it was found that the wings, which float for only a day or two by themselves, lessen the buoyancy of the fruit. Of fruits with both wings attached forty per cent. floated after two months, whilst of those deprived of the wings all floated after two months. In the ordinary course of flotation the wings in most cases break off during the first few weeks, and in the rough-and-tumble of current-transport this would occur sooner, so that the floating power of most of the fruits would not be much affected. The cause of the buoyancy in a structural sense belongs to the Convolvulaceous type. The kernel has no buoyancy, but it incompletely fills the cavity of the seed-vessel, the coats of which are quite waterproof, but have no independent floating power.

It is thus evident that like many other shore-trees Gyrocarpus Jacquini is distributed by the currents. It is not unlikely that its present sporadic occurrence in the Pacific islands may be due to the gradual extinction of the tree in this region, either on account of some insect pest introduced since Cook’s time or from the use of the timber for fire-wood by the aborigines.

SERIANTHES MYRIADENIA

This is a striking looking Acacia-like tree that might have been fitly discussed in the chapter on the enigmas of the Leguminosæ. Only four or five species are named in the Index Kewensis, of which one occurs in Malacca and in the Philippines, a second in New Caledonia, a third in Fiji, and the fourth, S. myriadenia, over the South Pacific groups of Fiji, Tonga, and Tahiti. Reinecke does not include the genus in the Samoan flora; and it is merely assigned to that group by Seemann on the authority of Mr. Pritchard, the British Consul in Fiji. Though common in the forests of the larger islands of Fiji, S. myriadenia is most at home on the banks of the estuaries, usually behind the mangrove belt, but not beyond tidal influence. The peculiar species, S. vitiensis, I found on the banks of the estuary of the Mbua River in Vanua Levu, the locality from which Gray described it. According to the French botanists, S. myriadenia, in Tahiti, ranges from near the sea to an elevation of 800 metres. The Fijian name of the trees is “Vaivai,” the name also of Leucæna Forsteri, and of some other introduced trees of the Acacia habit. The Tahitians apply the same name in the form of “Faifai” to S. myriadenia.

The Fijians value the trees on account of the wood; but unless the Polynesians were in the habit of transporting the seeds of their numerous timber trees, which is most unlikely, it seems at first sight useless to look to man’s agency for an explanation of the wide dispersal of a tree like S. myriadenia in the South Pacific. The tough, woody, indehiscent pods, from 3-1/2 to 4 inches long, floated in my sea-water experiments in the case of both S. myriadenia and S. vitiensis between seven and twenty-five days, after drying for some months. The seeds, about two-thirds of an inch (17 mm.) in length, are only freed by the decay of the fallen pod, and have no buoyancy. The agency of birds is evidently excluded; and it is, therefore, to the currents that we must make our final appeal; but their powers of dispersing the species appear quite insufficient to explain the occurrence of these trees in Tahiti. Perhaps, as in the case of Calophyllum spectabile, another Polynesian timber-tree found in Tahiti (see p. 136), man and the currents have worked together.

LEUCÆNA FORSTERI

This bush of the Mimoseæ frequents maritime sands in the South Pacific, and is confined to this region. It has been found in New Caledonia, Fiji, Tonga, Rarotonga, and Tahiti. The seeds sink and the pods dehisce on the plant, so that the agency of currents, unless we invoke the intervention of the drifting log, bearing the seeds in its crevices, seems to be excluded. Sea-birds might carry the seeds unharmed in their stomachs, but there is no evidence bearing on birds as agents in the dispersal of the species. Since the plant has not been recorded from localities outside the Pacific islands, and since it was collected by Cook’s botanists in Tonga and Tahiti, it cannot be placed amongst plants of recent introduction. Although growing on maritime sands in Fiji, Rarotonga, and Tahiti, it may grow inland, and according to Cheeseman is particularly abundant in Rarotonga. In Fiji it is apt to occupy newly-formed alluvial land at the mouth of the rivers, as in the case of the Rewa; but the “how and why” caused me much fruitless speculation, and I abandoned the plant in despair. The Fijians sometimes give it the native name of Serianthes myriadenia, which they then term “Vaivai ni Viti,” or the Fijian Vaivai. In Tahiti it is named “Toroire,” and in Tonga “Toromiro.”

MUSSÆNDA FRONDOSA

Mussænda frondosa is the only one of the sixty species of this tropical Asiatic and African genus that extends into Polynesia. This beautiful shrub, which is easily recognised by its conspicuous white, leaf-like calyx lobe, is common everywhere in Fiji, decorating, as Horne fitly remarks, in the contrast presented by its golden flowers, its large white calyx leaf, and its green foliage, many an acre of waste, grassy land, where the orange-coloured doves and the red and the green parrots flit to and fro. With its home in India, China, and Malaya, it ranges all over the South Pacific, from the Solomon Islands to Tahiti. Its berries contain an abundance of small, minutely-pitted seeds, 0·7 mm. or 1/35 of an inch in size, and weighing when well dried about 600 to the grain. The seeds retain after years of drying the property of clinging to passing objects by means of a few microscopic, thread-like fibres, that are attached to their surfaces. In this manner they will fasten themselves to the point of a knife, and the observer is astonished to see them dangling in the air from a pin’s point. I suppose that this is connected with some hygroscopic quality. At all events, it would enable these light seeds to be carried about not only by birds and bats but also by insects. It is possible that man has aided in the dispersal of this interesting plant; but birds, bats, and insects have, I think, mainly done the work.

LUFFA INSULARUM

This is regarded as a maritime form of Luffa cylindrica, a plant commonly cultivated throughout the tropics. The South Pacific plant, which occurs also in Australia and Malaya, has been found in New Caledonia, Fiji, Tonga, Rarotonga, and Tahiti. In Fiji it grows chiefly on the “talasinga” plains and in places once under cultivation. I noticed it in one locality climbing over the branches of an Inocarpus tree on the banks of the Rewa. In Rarotonga it is common in the lower regions. It is, according to Nadeaud, fairly frequent on the shore and in the lower valleys of Tahiti, where it was collected by Banks and Solander, the companions of Cook. The Pacific islanders, as far as can be gathered, make little or no use of the plant; and unless it was introduced accidentally with their cultivated plants, they could scarcely have been concerned in its dispersal.

In Fiji I made a special point of investigating the mode of dispersal of this plant. The fruits, which ultimately become dry and fibrous, are to be seen hanging vertically from the plant as it climbs among the branches of a tree. The apical disk usually falls off, and many of the seeds drop out through the hole thus produced; but a few remain entangled in the fibrous material occupying the interior of the fruit. I have noticed such fruits floating down the stream of the Rewa River; but my experiments showed that they do not float more than a week, whether in fresh or salt water. The seeds, however, possess a hard, impervious shell, and are well adapted to withstand unharmed prolonged immersion in the sea. They will evidently float for months. Out of one hundred selected seeds placed in sea-water, sixty were found afloat and sound after two months. The cause of the seed-buoyancy is purely mechanical. Neither the shell nor the kernel has any floating power, the buoyancy arising, as with Convolvulaceous seeds, from the unfilled space in the seed-cavity. When in Fiji, I tested the seeds of the ordinary cultivated tropical form of the plant which had been introduced into a garden from Australia. They all sank in a few days, and on being cut across the seed displayed but little unoccupied space in its cavity. I have no doubt that the Pacific form of this plant has been at times dispersed by the currents, not, however, through the fruits, but through the seeds. It is also quite possible that it may have been introduced by a pre-Polynesian people into the Pacific.

Summary of the Chapter

(1) Man in his distribution over the Pacific islands reproduces, but in a less degree, nearly all the difficulties presented by the plant in its dispersal. In both we have the age of general dispersion followed by a suspension more or less complete of the migrating movements; and in both we have differentiation associated with the isolation.

(2) The Pacific islanders possess two sets of food-plants. In addition to those commonly cultivated in our own time, such as the yam, the taro, the banana, &c., there are a number of food-plants now growing wild, but rarely cultivated, and only used when the others fail. These plants, which include the wild yams, the mountain bananas, Tacca pinnatifida, Pandanus odoratissimus, and several others, are regarded as older than the Polynesians in the Pacific, and as having probably formed the food of a pre-Polynesian race that practised only a rude sort of cultivation.

(3) The weeds of Polynesia also fall into two groups. In the first place there are the aboriginal weeds, of which those found in this region by Captain Cook’s botanists in the latter part of the 18th century are taken as examples. These include species of Urena and Sida, besides Waltheria americana, Oxalis corniculata, Bidens pilosa, and many other weeds. In the second place, there are the numerous weeds that are known to have been introduced by the white man since the voyages of the English and French navigators of Captain Cook’s time.

(4) There is reason to believe that many weeds now cosmopolitan in the tropics had obtained their present distribution in America and in the Old World before the Polynesians entered the Pacific. It is thus that we can explain how there existed in these islands at the time of their discovery by Cook, Bougainville, and other navigators of that period, a number of weeds that have their homes in America.

(5) It is not considered that the distribution of aboriginal weeds can materially aid the ethnologist in his study of the early history of man, since birds are regarded as the chief distributors of their seeds and fruits. Whilst man has prepared the conditions for the growth of weeds, the bird has usually brought the seeds.

(6) Amongst interesting plants concerned with man in the Pacific are Aleurites moluccana and Inocarpus edulis, which are regarded as in the main distributed through man’s agency. Gyrocarpus Jacquini is viewed as a tree originally widely dispersed by the currents in the Pacific, but now becoming extinct.

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XXIX. BEACH AND RIVER DRIFT

In the south of England.—On the coast of Scandinavia.—In the Mediterranean.—Southern Chile.—Very little effective dispersal by currents in temperate latitudes.—Cakile maritima.—In tropical regions.—River drift.—River and beach drift of Fiji.—Musa Ensete.—The coco-nut.—River and beach drift of Hawaii.—Comparison of the beach drift of the Old and New Worlds.—Summary.

THE BEACH DRIFT OF TEMPERATE LATITUDES

DISPERSAL by currents seems to be mainly restricted to warm latitudes. Whilst in the tropics seed-drift is abundant on the beaches, in the cooler regions of the globe it is usually very scanty and often masked by other vegetable débris.

Let us take, for instance, a beach in the south of England. We can find by careful searching amongst the stranded drift the seeds and seed-vessels of various littoral plants of the buoyant group, such as Arenaria (Honckeneya) peploides, Cakile maritima, Crithmum maritimum, Convolvulus soldanella, Euphorbia paralias, &c., and such sundries as bits of stems of Salsola kali bearing fruits; but their amount is scanty; and they are often difficult to find on account of the great amount of rubbish with which they are associated, such as empty stones of cherries, plums, and peaches; empty seeds of grapes; hazel-nuts, beech-nuts, chestnuts, acorns, all either empty or with decaying seed; the spiral pods of Medicago; besides quantities of leaves, sticks, and bark. Although the occasional shell of a Spirula, or the horny skeleton of a Velella, or a genuine pumice pebble (see Note 76), may tell us of long wanderings in mid-ocean, we find little that is not English or derived from neighbouring coasts on a beach in the south of England. I have examined numerous beaches on the coasts of Devon and Cornwall, and have never come upon any indubitable tropical seed-drift.

On one occasion I examined many of the beaches between Ilfracombe and Padstow with the object of finding tropical seeds, but to no purpose. Portions of bark, generally 2 to 4 inches across and much water-worn, together with a quantity of steamer-slag or cinders, often largely composed the stranded drift. No doubt this bark is stripped off by the waves from floating trees, which are generally stranded in a bare condition after a long ocean voyage. This is the case with the timber brought in the Oregon drift to Hawaii; and Sernander (p. 117) remarks that bark seldom occurs on the trees washed ashore with the Atlantic drift on the coasts of Scandinavia. Modern marine deposits ought to contain much bark débris.

On the beaches in the vicinity of estuaries we find a certain amount of river drift, and amongst it fruits or seeds of Sparganium ramosum, Iris pseudacorus, Alnus glutinosa, Rumex, and many other river-side plants, such as I have mentioned in my paper on the Thames drift (Journ. Linn. Soc. Bot., xxix). Most of them are capable of reproducing the plant, but not on the sandy beach where the waves have stranded them; and we thus see here one of the limits of the efficacy of currents as seed-dispersers.

From the labours of Lindman and Norman, the results of which are summed up by Sernander (p. 116) we can learn what are the components of the “Atlantic Drift” on the Scandinavian coast; and a strange assortment we here find, in which it is difficult to detect much indication of effective seed dispersal. Besides the seeds of Cæsalpinia Bonducella, Entada scandens, and Mucuna urens, familiar to us as occurring in the drift of tropical beaches, there is a quantity of vegetable drift hailing sometimes from North America, sometimes from the Canary Islands, and sometimes from the West Indies, mingled with much local drift in which the larch and steamer-slag or cinders predominate. The seed-drift derived from the proper beach-plants of the coast plays a subordinate part, though it is stated by Norman and others that seeds and seed-vessels, as the case may be, of Arenaria peploides, Cakile maritima, Convolvulus soldanella, and Lathyrus maritimus, with those of other plants, are also to be found.

The Mediterranean beach drift, as illustrated by the results of my examination of numerous beaches in Sicily as well as in the islands of Stromboli and Lipari, and of the beach at Cumæ, is of a scanty nature. If we eliminate the various evidences of cultivation which seem to occur over much of the temperate regions of the globe, very little remains of an interesting character. As in the south of England and in other regions, the empty stones of the cherry, plum, and peach, the empty nuts of the oak, hazel, &c., together with the spiral pods of Medicago figure largely in the drift; and here and there we come upon the seeds of littoral plants, such as Convolvulus soldanella and Euphorbia paralias.

I have found Medicago fruits in all these localities on the beaches. They often contain seeds, which, it may be added, have no buoyancy, the seeded pods themselves floating from two to five days. The pods of several kinds of Medicago form the great feature of Sicilian drift and are often indications in other places of the vicinity of cultivated districts. A small hairy species thrives on Letojanni beach near Taormina, and I observed its seeds together with those of Euphorbia paralias germinating in the drift stranded on the same beach. Arcangeli, in his Flora Italiana, enumerates as many as thirty-three species of Medicago. Many of the species grow in maritime districts, and their fruits must often get into the beach drift independently of cultivation. I noticed the pods amongst the drift brought down by the Alcantara, a river near Taormina, a fact which goes to explain their presence in beach drift.... On the beach of Trogilus Bay, near Syracuse, I gathered several fruits of a Vitex, apparently V. agnus castus. After being kept afloat for six weeks in sea-water some were placed in soil, when they soon germinated and reproduced the plant.

The beach drift of temperate Chile is described in Chapter XXXII. There, as in other beaches of cool latitudes, it is not easy to find seeds amongst the rubbish; but amongst the scanty seed-drift may be recognised much of what we are familiar with in the Old World, such as the seeds of Convolvulus soldanella, bits of the fruiting stems of Salsola kali, as well as the rubbish indicating the white man’s presence, such as empty stones of cherry, plum, and peach, Medicago pods, &c. In addition, we find the seed-vessels of plants like Franseria and Nolana that are peculiar to American beaches; and now and then, the seeds of Sophora tetraptera, a tree of the immediately adjacent hill-slopes, come under our notice.

Before quitting this subject of the beach seed-drift of temperate latitudes, it may be observed that when at San Francisco I visited the beach running south from the Golden Gate. With the exception of the fruits of Cakile maritima, a plant growing on the beach, few other seeds or fruits were observed in the drift.

The inference that there is very little effective dispersal by currents in temperate regions is of some importance, and Sernander arrived at a similar conclusion when discussing the origin of the Scandinavian flora. The few plants with buoyant seeds and fruits, such as Arenaria peploides, Cakile maritima, Crithmum maritimum, Convolvulus soldanella, Euphorbia paralias, and Lathyrus maritimus, are no doubt thus dispersed, and Norman is quite right in attaching some value to the distribution by currents of certain plants within the region of the Arctic flora; but after all it amounts to little, and geographical and climatic conditions have often had a predominant influence in determining the distribution in the temperate latitudes of littoral plants possessing buoyant seeds or fruits.

Nowhere is this shown more plainly than with the littoral plants with buoyant seeds or seed-vessels that are found on our English beaches. Some have evidently acquired their present distribution before ice and snow reigned supreme in the extreme north. Though it may be possible, it seems highly improbable, that either Arenaria peploides or Lathyrus maritimus, both of which occur on beaches in high northern latitudes in the Atlantic and Pacific Oceans (as in Arctic Norway, Spitzbergen, and Behring’s Straits), could possess in our own day any means of communication between their areas of distribution on the borders of these two ocean-basins.

So again with Cakile maritima, the occurrence of this or of two closely allied species on both sides of North America cannot be attributed to any present working of the currents for two reasons. In the first place, as is remarked in Note 18, the results of two independent experiments made by me show that the fruits will not float more than a week or ten days in the sea, a capacity that will not admit of their transportation by the currents over tracts of ocean more than one or two hundred miles across. In the second place, this species is not an Arctic plant like Arenaria peploides and Lathyrus maritimus; and the possibility of inter-communication between the Atlantic and Pacific Oceans having any effective value from the standpoint of dispersal, shadowy as it is with the two Arctic species, is still more so in the case of Cakile maritima. Norman’s observations on the coast of Norway, as quoted by Sernander (page 123), indirectly indicate how hopeless it would be for this plant to attempt to traverse the Arctic region. Just as I have noticed on the north coast of Devonshire, the fruits occur plentifully in the beach drift and germinate freely in the upcast wrack as far north as Senjen in latitude 69°. Further north the plant has been recorded from only eight localities, and since it is there sterile and but a summer annual, the seed-vessels, it is argued, must have been brought by the currents from the south.

The reference to Cakile maritima as a summer annual on the north coast of Norway is of interest; but I may point out that it displays a similar behaviour in England on the north coast of Devonshire. Here, during the latter half of July, 1903, I found the fruits common in the stranded drift, and often in a germinating condition, whilst numerous seedlings one to two inches high with the fruit-shell still attached were growing out of the sand. From this arises the curious reflection that an annual which germinates in the end of July could scarcely be expected to mature its fruit before the winter. It would seem that this beach plant hampers its own dispersal by its misdirected efforts; and the idea suggests itself that we have here the explanation of its sterility in the north of Norway. Had it been a perennial like Arenaria peploides and Lathyrus maritimus it might have had a similar distribution within the Arctic Circle.

Quite other considerations seem to be suggested by the perennials Crithmum maritimum and Euphorbia paralias. In these cases, although the seeds or fruits, as the case may be, will float for months in sea-water without apparently sustaining any injury, the species are confined to the warmer parts of the European region.

From Convolvulus soldanella we obtain another story. Its occurrence in the temperate regions of both the northern and southern hemispheres, great as the floating powers of the seeds may be, is concerned with something more than with questions relating to modes of dispersal. The circumstance that in its distribution in the temperate regions it is practically coterminous with Ipomœa pes capræ in the tropics is very significant (see Note 49).

Each one of the English beach plants with buoyant seeds and fruits has its own story of the past to tell. Time has indeed gathered on our beaches current-dispersed plants, which, if they could speak, would tell us strange stories of many latitudes, stories of change within the Arctic Circle, and stories of great events within the temperate regions, and, as in the case of Convolvulus soldanella, stories of a past within the tropical zone. It cannot be said that investigators lack clues leading to lines of inquiry into the age that immediately precedes our own.

Yet valuable as our British plants would be for this purpose, they do not afford any indication that currents have played an important part in plant distribution in temperate and arctic latitudes. Ekstam strikes the true note for these regions when discounting the agency of currents in the instance of the Spitzbergen flora, he regards the wind as the greatest factor in seed-dispersal and after that the bird. The several interesting points raised by this botanist are discussed in Chapter XXXIII.

THE BEACH-DRIFT OF TROPICAL LATITUDES.

Tropical beaches, as a rule, present a much greater abundance and variety of stranded seeds and fruits than we find on beaches in temperate latitudes. Observers in different parts of the tropics have alluded to the enormous amount of vegetable drift floating in the sea off the coasts, particularly in the vicinity of estuaries. Though much of it is brought down by rivers, a good proportion is also derived from the luxuriant vegetation that lines the beaches. Gaudichaud speaks of the immeasurable quantity of drift (trees, branches, leaves, flowers, fruits, and seeds) floating amongst the islands of the Molucca Sea; and Hemsley, who quotes this author, gives other facts illustrating the same point. Moseley tells us that seventy miles off the coast of New Guinea, H.M.S. Challenger found the sea in places blocked with drift (Bot. Chall. Exped. iv. 279, 284). When the author of this book was in the Solomon Group, long lines of vegetable drift were frequently observed floating among the islands. The Rewa River in Fiji carries down a great amount of drift to the sea; and as described in Chapter XXXII, the Guayaquil River in Ecuador bears seaward an enormous quantity of these materials.

When we come upon this floating drift out at sea off an estuary, we find, as Mr. Moseley pointed out, that the leaves have gone to the bottom, whilst the floating islets, composed of the matted vegetation lifted up from the shallows of a river channel, which form such a feature in the Guayaquil River, have been dispersed or sent to the bottom. However, a very large proportion of the seed-drift brought down by a river from the interior has no effective value for the purposes of dispersal. Many of the fruits and seeds brought down from inland owe their presence in river-drift entirely to the buoyancy acquired by the decay of the seeds. It is in its lower course when it traverses the mangrove belt that a river picks up most of the material that is of service in distributing the species; and this is mingled out at sea with the numerous buoyant seeds and fruits of littoral plants that are swept off the beaches by the currents.

A description is given in Chapter XXXII of the enormous amount of vegetable drift brought down by the Guayaquil River to the coast of Ecuador. Besides the huge tree-trunks and the floating Pistias, we observe large islets formed mainly of Pontederias and Polygonum, together with a host of seeds and seed-vessels, both large and small, including those of Anona paludosa, Entada scandens, Erythrina, Hibiscus tiliaceus, Ipomœa, Mucuna, Vigna, &c., accompanied by the empty seeds of Phytelephas macrocarpa and of many other strange plants from the slopes of the Chimborazo mountains. In addition, we notice the seedlings of Avicennia and of Rhizophora mangle together with the seeded joints of Salicornia peruviana and the germinating fruits of Laguncularia.

When in Fiji I made an especial study of the drift of the Rewa Estuary within tidal influence, the results of which are incorporated in various parts of this work. In the rainy season, when the drift is most abundant, the following would be its most characteristic components:

Seedlings of Bruguiera and Rhizophora. Fruits of Barringtonia racemosa and B. speciosa, the first-named most abundant and often germinating. Seeds of Carapa obovata, most of them far advanced in germination. Fruits of Lumnitzera coccinea. Fruits of Cerbera odollam, abundant. Fruits of Inocarpus edulis, with the seed generally rotten. Fruits of Heritiera littoralis, Parinarium laurinum, and Pandanus. Empty seeds of Aleurites moluccana. Fruits of Scirpodendron costatum, abundant. Fruits of Clerodendron inerme and Smythea pacifica, both of them in some cases germinating. Pyrenes of Morinda citrifolia. Small fruits of Vitex trifolia and Premna taitensis, both sometimes abundant. Seeds of Entada scandens, Mucuna, and Vigna lutea. Pods of Dalbergia monosperma and Derris uliginosa, the last sometimes in a germinating condition. Seeds of Hibiscus tiliaceus and of different species of Ipomœa, such as I. peltata and I. pes capræ.

Amongst other seeds and fruits brought down by the Fijian rivers and stranded with a large amount of miscellaneous vegetable débris on the beaches in the vicinity of the estuaries are the seeds of Dioclea, Strongylodon lucidum, and Afzelia bijuga; the empty seeds of Musa Ensete (as identified with a query at Kew); the empty stones of the Sea tree, apparently a species of Spondias; the seeds of Colubrina asiatica; the fruits of an inedible indigenous Orange (Citrus vulgaris?) referred to in Chapter XIII; the cocci of Excæcaria Agallocha and Macaranga; and Coco-nuts.

The occurrence in Fijian beach-drift of the seeds of Musa Ensete, or of a wild banana much like it, is very remarkable. This species is found in the mountains of Abyssinia and on the slopes of Kilima-njaro in Equatorial Africa; but according to the monograph by Schumann on the Musaceæ (Engler’s Pflanzenreich, 1900) the species is confined to Africa, whilst all the other species of the subgenus are mostly restricted to the same continent with the exception of one or two in Further India. The empty seeds are frequent on the beach at Duniua at the mouth of the Ndreke-ni-wai in Savu-savu Bay, Vanua Levu, and are doubtless brought down by that river. Strangely enough the natives could give me no information about the parent plant which I never discovered. The seeds did not come under my notice in any other locality in Fiji. They answer to the description and to the figure given by Schumann for Musa Ensete; and their presence in the drift is one of the mysteries of the Pacific floras.

To enumerate the seeds and fruits found stranded on beaches in Fiji would be to give a list of all the littoral plants with buoyant seeds or fruits that are included in the list given in Note 2. I may here allude to the fact that the Coco-nut, whether brought down by a river or transported by a current, is able to germinate and establish itself when washed up on the Fijian beaches. I have found these fruits germinating amongst the drift stranded on the beaches near the mouths of rivers, some just beginning to germinate and others already striking into the sand and showing the first leaves. White residents living for years in one locality were quite convinced that this frequently happens. One of them pointed out to me some newly formed land at a river’s mouth, not over two years old, on which were growing young plants three or four feet high of Barringtonia speciosa, Calophyllum Inophyllum, and several other plants including young Coco-nut palms, all growing from fruits washed up by the waves and therefore self-sown.

Like the littoral flora the beach-drift proper to the Hawaiian Islands is very scanty. This is due to the scarcity of rivers, to the absence of the mangrove-formation from which much of the drift is derived in other tropical regions, and to the paucity of shore-plants with buoyant seeds or fruits. As is observed in Note 30, where the composition of the beach drift is described, the presence of a large amount of timber and of other materials brought by the currents from the north-west coast of America masks much of the local drift.

Remarks on the beach-drift of the Panama Isthmus, and of the Ecuadorian, Peruvian, and Chilian coasts of South America will be found in Chapter XXXII. I have examined beach drift in other tropical regions, as in the Solomon group, on Keeling Atoll, and on the south coast of West Java; whilst there are at my disposal the data supplied by Schimper and Penzig for the Malayan region including Krakatoa, and by Hemsley for tropical regions generally. It will, I think, be best, if instead of describing in detail the composition of the drift for each locality, I refer briefly to the features that distinguish the tropical beach-drift of the Old World from that of the New World.

The beach-drift reflects the characters of the coast flora; and since tropical littoral floras belong to two great regions, the Asiatic including Polynesia and the African East Coast, and the American including the African West Coast, the seeds and fruits stranded on the beaches may be similarly referred to the same two regions.

All over tropical Asia, as well as in the tropical islands of the Indian and Pacific Oceans, the drift stranded on the beach presents the same general character, and as a rule possesses seeds and fruits of the same species that range over the whole or the greater part of this region. Almost everywhere we find seeds or fruits of the same plants of the beach formation, such as Barringtonia speciosa, Cæsalpinia Bonducella, Calophyllum Inophyllum, Canavalia obtusifolia, Cerbera Odollam, Cordia subcordata, Entada scandens, Guettarda speciosa, Hernandia peltata, Hibiscus tiliaceus, Ipomœa pes capræ, Mucuna, Scævola Kœnigii, Sophora tomentosa, Terminalia Katappa, and Tournefortia argentea. In those localities where mangrove-swamps occur we find generally diffused in the stranded drift of this region the seedlings of Bruguiera and Rhizophora, the seeds of Carapa moluccensis, the fruits of Heritiera littoralis and Lumnitzera coccinea, and the pods of Derris uliginosa. Amongst sundries found over much of this region may be mentioned, the drupes of Pandanus, the seeds of Erythrina, Vigna lutea, and Hibiscus tiliaceus, and the “nuts” of Aleurites moluccana. With the exception of the last-named all the fruits and seeds here enumerated are effectively dispersed by currents over great areas. The sound nuts of Aleurites have no buoyancy; and the nuts only acquire their floating power through the decay of the kernel (see p. 419).

The beach drift of the American region, a region which comprises both the Pacific and Atlantic coasts of tropical America as well as the African West Coast, has some features in common with the Asiatic beach-drift and other features peculiar to itself. The plants, however, that are represented in the drift of both regions are comparatively few, and none of the large fruits of the Asiatic region are here to be noticed. We observe, however, that the drift of the two regions possess in common the seeds of Cæsalpinia Bonducella, Canavalia obtusifolia, Entada scandens, Erythrina, Mucuna, Sophora tomentosa, and Vigna lutea, all belonging to the Leguminosæ; and to these we must add the seeds of Hibiscus tiliaceus and of Ipomœa pes capræ, and the seedlings of Rhizophora and Avicennia. (Avicennia occurs in tropical Asia, but not in Polynesia.) The distinctive characters of the beach-drift of both coasts of America and of the west coast of Africa would be shown in the presence of seeds of Anona paludosa, the fruits of Laguncularia racemosa, Conocarpus erectus, Spondias lutea, and other plants. But the beach-drift of the American region is much more scanty. Of the shore plants generally dispersed in this region there could not be more than a couple of dozen that are indebted for their wide dispersal to the currents, and these alone figure in the effective beach drift. In the Asiatic region these plants would number at least seventy or eighty.

Summary.

(1) Effective dispersal by currents is mainly restricted to warm latitudes, as is indicated by the scanty character of the seed-drift stranded on the beaches of the south of England, Scandinavia, the Mediterranean, and Southern Chile.

(2) The present distribution in temperate latitudes of littoral plants possessing buoyant seeds or seed-vessels is to be attributed more to the influence of geographical and climatic conditions than to the agency of currents. With some of them, such as those that occur on both sides of North America, it is evident that their distribution antedates the present climatic conditions within the Arctic Circle.

(3) Time has gathered on an English beach current-dispersed plants that could tell us strange stories of many latitudes.

(4) The seed-drift that is often found in such abundance in tropical seas is partly brought down by rivers and partly swept off the coast. Very little of the seed-drift brought down by the rivers from the interior is of any service for plant-dispersal, nearly all the floating seed-drift found at sea which has any effective value being derived from the plants of the beach and of the mangrove belt.

(5) The tropical beach drift of the Old and New Worlds reflects the characters of the littoral floras of those regions, more especially with regard to the plants provided with buoyant seeds or seed-vessels. The plants represented in the beach drift common to both these regions belong mostly to the Leguminosæ. The large fruits so characteristic of Old World beach-drift are not found in the New World. The number of shore plants with buoyant seeds or seed-vessels that are widely dispersed in the American region are only one-quarter or one-third of those in the Old World region; and this difference is reflected in the scanty character of tropical American beach-drift.

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