European animals : their geological history and geographical distribution

Front matter

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Irish Scenery with the Irish Hare (Lepvs timidus ) and Grouse ( Lagopus scot tens ) in the Foreground. Photographed from a life group in the Dublin Museum.

Preface

The method of treatment of the subject discussed in this work was adopted by me when delivering the Swiney Lectures on Geology last year, at the Victoria and Albert Museum in London.

Dr. Wallace’s remark that we may be enabled, by an accurate knowledge of any group of birds or insects and of their geographical distribution, to map out the islands and continents of a former epoch, encouraged me to attempt to apply his ideas in dealing with our own Continent, and to extend them to other groups of animals.

Professor E. Forbes was the first to recognise the significance of the geographical distribution of living animals in deciphering their past wanderings, and I have approached the investigation of the geological history of our fauna in the manner indicated by him. I thought that this method would convey to the general reader, as well as to the student, a clear conception of the nature of the problems to be solved.

I trust that this work will stimulate the researches of the student of systematic Biology and that it may also prove acceptable as a contribution to the past geographical history of our Continent.

Professor Ray Lankester, the Director of the British Museum (Natural History), urged me to publish my lectures, and promised me every facility in suitably illustrating this work by photographs taken from specimens in his charge. I have

PREFACE.

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availed myself of this kindness in many instances. My gratitude is also due to Messrs. Th. G. Fisher, to Messrs. Macmillan, to H.M. Stationery Office, and to Mr. Madison Grant for allowing me to copy illustrations from works issued by them.

To the many friends who have given me information or assistance I beg to tender my sincere thanks. Especially am I indebted to Sir Henry Howorth, who not only read through my rough proofs, but was good enough to make numerous corrections and critical notes, which were most valuable to me. Dr. F. Oswald, the author of the recently published work on the Geology of Armenia, suggested some additions, while Mr. W. E. Sharp, Mr. W. Evans, Mr. A. S. Kennard, Mr. Robert Welch, Mr. R. Le Praeger, Mr. T. W. Lyster and Mr. J. X. King gave me valuable assistance or information.

In laying this work before my readers, I am conscious of its many defects, arising to some extent from the wide range of the subject. It leaves many points inadequately treated. But I venture to hope that naturalists will assist me in rendering my future researches more complete by sending me notes of any important omissions or corrections.

R. F. S.

Tudor House,

Dundrum, Co. Dublin, January 17 th, 1907.

Chapter I. Introductory

PAGE

Geological history of animals founded upon their present and past geographical distribution — Accidental or occasional means of dispersal — Importance of mammals and molluscs in tracing the history of animals — The founders of modern zoogeography — Importance of the British Islands as a starting-point to an enquiry into the geological history of European animals — Methods of research to be adopted in tracing species to their place of origin i — 25

Chapter II. Ireland

Irish freshwater animals and relict lakes — Absence in Ireland of familiar English species of animals and plants— Presence of such showing a south-western European range, and of others indicating relationship with North America and the Arctic regions — Mingling of southern and northern animals and plants now and in the past — Geographic; 1 evolution of Ireland and its climate . 26 — 47

Chapter III. Scotland

Importance of northern forms of animal life in Scotland as compared with Ireland — Western or American and southern elements — The extinct fauna of Scotland — English animals penetrating to Scotland— Animals and plants of the Shetland and Faroe Islands, and of Iceland— Former land connection between Scotland and Iceland 48—68

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CONTENTS.

Chapter IV. England And Wales

PAGE

Relative importance of northern, southern and eastern species — Germanic group — Extinct animals of eastern origin — Lusitanian species — Endemic species — Summary of results obtained from study of Irish, Scottish and English animals and plants — Effect of Glacial Period on animal life in the British Islands — Marine faunas and their evidence with regard to former changes of shore-line . 69 — 87

Chapter V. The Spanish Peninsula

Faunal divisions of the Peninsula — The Lusitanian fauna — Spreading of species from the Peninsula into eastern and northern Europe —

The Pyrenees — Relationship between the faunas of Marocco and Southern Spain — The Balearic Islands — Relationship of the animals of Madeira and the Azores to those inhabiting the mainland — The Atlantis problem 88 — 105

Chapter VI. Scandinavia

Effects of the Glacial Period on the animals of Scandinavia — Causes of animal migrations — South-western fauna and flora — History of the flora, and different views of botanists — The fauna and flora of Greenland — Connection of Greenland with Northern Europe and Arctic North America — The Baltic Sea and its origin — Former land connection between Scandinavia and Scotland . 106 — 127

Chapter VII. The Alps

Similarity of Arctic and Alpine faunas — Geological history of Alpine area — Different elements in the fauna and flora — Asiatic influence on the Alpine fauna — Southern relicts — Lake of Geneva and its relict forms — Alpine plants, their origin and dispersal . . 128 — 145

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Chapter VIII. Eastern Europe And The Caucasus

PAGE

Evidences of an invasion of eastern Europe from Siberia — Former extension of the Aralo-Caspian basin towards the Polar Sea — Steppe and tundra faunas in Europe — The Caspian Sea and its fauna — The fauna of the Caucasus and its origin — The Crimea a peninsula of the Caucasus -On the origin of the Black Sea and its fauna — The Carpathian mountains and Transylvania . 146 — 165

Chapter IX. Western Plain Of Europe

Steppe and tundra faunas in the west — Fossil remains of African animals — Influence of northern barrier on advance of southern and eastern species — Origin of some western European species — Distribution of birds — The river system of middle Europe — Botanical survey of the district 166 — 192

Chapter X. Eastern Mediterranean Region

Faunal relationship of Palestine with Africa and Europe — Former land-connection between Asia Minor and Greece — The Black Sea isolated from the Mediterranean — The Greek Islands— The Balkan peninsula as an important centre of distribution — Former geographical mutations in Italy and the Adriatic Sea — The Mediterranean Sea composed of two distinct basins — Their recent geological union 193 — 21 1

Chapter XI. Western Mediterranean Region

The early Tertiary fauna and flora of Italy — The fauna of Sardinia and Corsica — The Tyrrhenian province — Plant distribution in the eastern and western Mediterranean — The faunal relationship between Sicily, Malta, and Tunis — North Africa a part of Europe — The Canary Islands 212 — 230

LIST OF ILLUSTRATIONS.

FIG. PAGE

Irish Scenery, with Irish Hare ( Lepus timidus) and Grouse ( Lagopus scoticus ) Frontispiece

1. Platyarthrus Hoffmanseggii. with map of Europe ... 6

2. Mountain Avens ( Dryas uctopetela) ...... io

3. Map of the British Islands indicating floral divisions (after E.

Forbes) .12

4. Pleistocene Europe (after Professor Boyd Dawkins) . . .21

5. Badgers ( Meles taxus) 24

6. Pollan ( Coregonus pollan), with map of the British Islands

indicating former geographical condition .... 28

7. Strawberry tree (A rbut-us unedo), with map of Europe . . . 30

8. London-pride (Sax if rag a umbrosa), with map of Europe . . 31

9. Freshwater pearl Mussel (Margaritana margaritifer), with map

of the World 35

10. Slender Naiad (Naias Jlexilis) ....... 36

11. Great Auk (A lea impennis), with map of the World ... 38

12. Pelophila borealis, with map of the British Islands ... 42

13. Map of probable former conditions in the British Islands . . 46

14. Rhopalomesites Tardyi, with map of the British Islands . 50

15. Bristle Fern ( Trichomanes radicans), with map of the World . 52

16. Anarta melanopa, with map of Europe 53

17. Irish Elk ( Cervus giganteus), with map of Europe and Asia . . 55

18. Lepidurus glacialis, with map of Europe and Asia 57

19. Mole (/ alpa europaea), with map of Europe and Asia . . 59

20. Roedeer ( Capreolus caprea), with map of Europe .... 61

21. Arianta arbustorum, with map of Europe ..... 65

22. Succinea groenlandica 66

23. Testacella maugei, with map of the British Islands ... 71

24. Roman Snail (Helix pomatia), with map of Europe . . 74

25. Hamster (Cncetus frumentarius), with map of Europe . . 76

26. Hippopotamus ( Hippopotamus amphibius), with map of Europe . 78

27. Eulota frutiemn, with map of Europe and Asia .... 80

28. Spotted Slug ( Geomalacus maculosus), with map of Europe . . 8g

29. Map indicating the range of genus Arion ..... 91

30. Clausilia Pauli 95

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LIST OF ILLUSTRATIONS.

FIG.

31. Elona quimperiana, with map of Western Europe

32. Moorish Gecko (Tarentola mauritanica) . ... .

33. Tudora ferruginea

34. Dipper ( Cinclus cinclus )

35. Reindeer (Rangi/er tarandus), with map of the World .

36. Arctic Fox ( Vulpes In gap us) . . . . . . • .

37. Lemmings (Letnmus lemmus and Dicrostonyx torquatus) .

38. Patula rotundata, with map of Europe

39. Patula ruderata, with map of the World .

40. Maps of North-western Europe and Greenland I.

41. Maps of North-western Europe and Greenland II.

42. Pomatias obscurus

43. Apollo Butterfly (Paniassius Apollo ), with map of Europe

44. Chamois (Rupicapm tragus), with map of Europe

45. Alpine Marmot (Arctomys marmotta), with map of Europe .

46. Range of Arctic Hare ( Lepus titnidus) ......

47. Great Jerboa (A lactaga saliens), with map of Europe .

48. Fish Louse [I do tea entomon) ........

49. Mysis relicta, with map of Europe

50. Cyclotus Sieversi, with map of Europe and Asia

51. Saiga Antelope (Saiga tatarica)

52. Striped Hyaena ( Hycena striata), with map of Europe .

53. Spotted Hyaena ( Hycena crocuta), with map of Europe

54. Lion (Felis leo), with map of Europe ......

55. Mammoth ( Elcphas priinigenius), with map of the World

56. Map indicating past range of the Lion and Saiga Antelope in

Europe

57. Freshwater Tortoise ( Emys orbicularis), with map of Europe

58. Viper ( Vipera bcrus), with map of Europe and Asia

59. Pupa cylindracea, with map of Europe

60. Hooded Crow ( Corvus cornix), with map of Europe and Asia

61. Black Crow ( Corvus corone), with map of Europe and Asia

62. Freshwater Crayfish ( Potamobius pallipes) . ... .

63. Map of the Eastern Mediterranean

64. Map of the Balkan Peninsula and Asia Minor in past times

65. Praying Insect {Mantis religiosa)

66. Range of the genus Clausilia in Europe

67. Freshwater Crab ( Pvtamou cdulis ), with map of the Mediterranean

region

68. Porcupine ( Hystrix cristata), with map of Europe and North

Africa

69. Rnmina decollata, with map of Europe

70. Parmacella Olivieri, with map of the Mediterranean region

I’AGE

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•34

•49

•54

•56

•59

168 170 172 •73

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EUROPEAN ANIMALS.

Chapter I

The geological history of our animals is largely the history of their past wanderings. And just as in geology the study of the present supplies us with a key that opens the secrets of the past, so a search for the nature of the bygone wanderings of our animals is revealed to us by their actual geographical distribution. By carefully observing how the dispersals of animals are brought about nowadays, we are enabled to judge of the dispersals of the past.

A great many noteworthy facts have been collected together by Lyell, Darwin1 and others, to demonstrate the facilities possessed by species for accidental or occasional means of dispersal. For, though Darwin admitted that great mutations of land and sea had occurred within the period of existing organisms, he paid a good deal of attention to experiments illustrating the possibility of lighter objects, such as sdeds, insects or shells, being carried by marine currents across the sea from the mainland to an island.

With the view to testing his theory, Darwin immersed a number of specimens of the Roman snail (Helix pomcitia) (Fig. 24) in seawater, and found some of them to withstand an immersion for twenty days. During this length of time, he remarks, the shell might have been carried, by a marine current of average swiftness, to a distance of 660 geographical miles.

After all these experiments, Darwin acknowledged that it did not seem to him likely that land shells had often been transported in that way across the sea to an island. He suggested

1 A list of the books and papers consulted in preparing this volume will be found in the Appendix.

E.A.

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EUROPEAN ANIMALS.

that possibly young snails might sometimes adhere to the feet of birds, and thus be carried to long distances from their home.

Baron Aucapitaine has since tried similar experiments, which have been even more successful. He immersed a dozen specimens of another mollusc ( Cyclostoma elegans) in sea water for a fortnight, and out of these eleven survived. This snail possesses a lid or operculum, with which it can close the mouth of its shell, and this fact no doubt contributed to the remarkable success of Aucapitaine’s experiment.

We may take it for granted that owing to its possession of an operculum this snail is endowed with exceptional facilities for being carried from the western parts of Europe, where it is common, to distant islands. And yet it does not inhabit the Canary Islands, Madeira, or even Ireland, none of which are at too great a distance to be within easy reach for a floating object. The fact that this shell does not occur living in Ireland is of particular interest, because dead shells have frequently been picked up on its shores, indicating that marine currents actually do carry specimens, and have probably transported living ones to that island for many centuries. That Cyclostoma elegans has nevertheless failed to establish itself in Ireland seems to justify the belief that other snails less adapted for ocean transport, or slugs, would have no chance of doing so.

As for Darwin’s theory that birds might occasionally carry young snails on their feet across the sea, this subject has been very carefully investigated since his time. It has been shown by Mr. Winge and Dr. Andersen, who have examined the legs and wings of many thousands of migratory birds just after crossing the sea, that their legs were clean ; and no seeds or other objects were found adhering to their feathers, beaks or feet. It has also been proved that birds migrate on empty stomachs.1

After years of patient research on the origin of the fauna of Celebes, Dr. Sarasin came to the same conclusion : that birds are of little importance in influencing the dispersal of other animals.

1 Dr. Knud Andersen of Copenhagen informed me of these facts by letter.

INTRODUCTORY.

Although the occasional or accidental transport of species by wind or by marine currents has probably taken place sometimes, it does not as a rule seem to affect the constitution of an island fauna very materially. The influence of man, however, on a fauna is an important factor.

Mr. Ivew, who has occupied himself specially with the subject of accidental distribution, and whose little book on the subject is well known, is of opinion that, as far as mollusca are concerned, human agency has influenced their dispersal more than all other causes taken together. Man is probably the most powerful of all agents in the occasional transmission of species across natural barriers, and his actions may be accidental as well as intentional. Hence among animals possibly introduced by man we have to distinguish between those disseminated all over the world by pure chance and such as have been carried into new countries purposely. Snails, centipedes, woodlice, beetles and cockroaches are constantly being unintentionally carried with vegetables, fruits and shrubs from one country to another. Earthworms are sometimes transported in the balls of earth in which the roots of trees are enveloped.

Very frequently the animals which have been thus introduced from one country to another fail to permanently establish themselves. They sometimes linger on for a few years and then die out again. Occasionally, however, they reach suitable surroundings, and spread rapidly. As an example, I might mention our large garden snail, Helix aspersa, which is used as food by French and Portuguese sailors, and which has been exported to many foreign countries where flourishing colonies now exist.

As a rule, such intruders to the native fauna are readily recognisable, for they scarcely ever extend their range very far from human habitations. They are known now from almost every country in the world. But we must carefully guard ourselves against the conception that all cosmopolitan forms of animal life must necessarily belong to that class of human importations.

The mere fact of an animal possessing a wide range proves

B 2

EUROPEAN ANIMALS.

its adaptability to varied climates, and frequently betrays its ancient origin.

It is quite possible, therefore, that many of our widelydistributed forms may owe their cosmopolitan range to the fact of their being very ancient. The genus Pupa, a small turret-shaped snail with a world-wide range, was already represented in the carboniferous deposits of North America. Another landshell, called Conulus, from the same formation, likewise enjoys an extensive range. Some fresh-water species can be traced back to the Cretaceous period. In the countless ages which have passed since then, it is no wonder that certain animals should have acquired a world-wide range.

We may regard it, therefore, as an established fact that accidental dispersal of a species is the exception, while slow progress on land for terrestrial animals is the rule.

As far as possible, I shall refer to well-known animals, in these studies of the European fauna, for it is obvious that I can only mention a mere fraction of the immense number of species to be found on our Continent. Sometimes, however, I shall allude to such animals which appear to me of particular importance from a distributional point of view, though they may be inconspicuous and more or less unknown to the great majority of my readers.

Every species of animal has its own area of geographical distribution, to which it is, as a rule, permanently confined. It will naturally tend to increase the boundaries of its range in every direction, unless prevented from doing so by some barrier which may be either a mountain range, a desert or the sea. The latter is the most formidable barrier.

When we find such a close relationship in the faunas of two countries as between those of England and France, or Greece and Asia Minor, we may be sure that the sea barrier which now exists was absent when the animals crossed from the one area to the other. Similarly when we notice a very striking difference in the fauna of two parts of a country, such as between southern and northern Spain, which cannot be explained from its present configuration, we may assume that

INTRODUCTORY.

a powerful barrier formerly existed which separated these two areas. We can thus ascertain the gradual changes which have occurred in the distribution of land and water in Europe. From a careful study of the general range of groups of species, we can gather also the direction of their advance. We have been able to trace, in this manner, that large assemblages of animals issued from various parts of Europe, invading new territories like conquering armies, and sometimes after their retreat leaving a few stray members behind as a standing testimony of their former invasions.

Island faunas are particularly useful in aiding us to estimate the comparative ages of such waves of invasion, for they frequently preserve the traces of the latter much longer than the continents, where, owing to keener competition, faunas are subject to more rapid modification.

We need not use for our purpose species of animals which might owe their dispersal to such accidental means as I alluded to.

For instance, in the nest of the small yellow ant, which lives in this country, as a rule, under stones or clods of earth, we frequently meet with a minute white woodlouse (. Platyarthrus H offmanseggii) (Fig. i). It lives in company with the ants and is unmolested by them. The latter apparently do not provide for it in any way, though it is quite blind. Now the same species of woodlouse occurs again in the burrows of the yellow ant in France. Here is a case, then, of a small and inconspicuous object, which yet could not possibly have passed from the one country to the other except by means of some former continuity of land.

I have now endeavoured to give some of the reasons for my belief in the profound importance of the present geographical distribution of animals as an indicator of their geological history. But we possess still other means to aid us in unravelling the history of our European fauna.

Though it is evident that, in the vast majority of cases, land and fresh-water animals leave no perceptible trace of their former presence, yet much has been preserved to us, and these

Fig. i. — Platyarthrus Hoffmanseggii, with its geographical distribution in Europe

MARKED IN BLACK.

INTRODUCTORY.

remains are, of course, of immense value in our researches. It is especially the river and lake deposits which have yielded the remains of animal life. But the numerous caverns in limestone districts which have either offered shelter to various kinds of wild animals or which have been used by wolves, wild cats or hyjenas as convenient store-houses for their prey, have preserved for us some valuable chapters of history.

These evidences of past distribution aid us materially in tracing the wanderings of our animals from one part of Europe to another, or even from beyond the boundaries of our Continent.

This leads us, then, to the consideration of the comparative importance of the various classes of animals as aids to historical zoogeography.

Mr. Lvdekker is one of the chief supporters of the doctrine that mammals afford us the safest and truest indications of the latest changes which have taken place in the distribution of land and water, and no one can help appreciating the force of his arguments in their favour, after reading his very instructive work on the geographical history of mammals. Their present and past range in Europe, moreover, is now fairly well known, though many details still require to be worked out.

In some respects the snails are even of greater value, for the shells, left behind them after death, are readily preserved and identified ; and many of the species, as I have pointed out, are of very great antiquity. Snails are bound to the soil almost unlike any other creatures, while their organs of locomotion are of a primitive nature. They are mostly indifferent to the nature and quality of the food supply or the conditions of climate, and can exist and spread under more adverse conditions than mammals. They are easily collected and studied, with the result that our knowledge of the geographical distribution of European snails and slugs is probably more complete than that of any other class of animals.

Nevertheless, other naturalists claim for their favourite groups that they deserve some recognition in ranking as important guides in geographical studies of the past.

Mr. Beddard has a good word to say on behalf of the

EUROPEAN ANIMALS.

earth-worms, while Mr. Pocock makes an appeal for scorpions. Dr. von Ihering vindicates a claim for ants, Mr. Andrew Murray for beetles, and Dr. Ortmann for fresh water crayfish.

As a matter of fact, in all classes of the animal kingdom there are certain families or genera which, on account of their peculiar habits or mode of life, are eminently suitable as indicators of former changes in land and water.

Though we naturally connect Wallace with the foundation of the science of modern zoogeography, as the geographical distribution of animals is sometimes styled, Edward Forbes and Sir Charles Lyell forestalled him in many respects. Thus the doctrine of specific centres of distribution of plants and animals was put by Forbes to a practical test long before Wallace had made this branch of natural history his special study. It is particularly in connection with the geographical distribution of the animals of our own country that Edward Forbes became so deservedly famous.

Dr. A. R. Wallace gained his reputation in the East in the Malay Archipelago, and on his return he published not only his delightful and instructive travels, but his great works on “The Geographical Distribution of Animals ” and on “Island Life.” What his views were upon the subject I am discussing may be gathered from the following remark which he made in one of his earlier works: “ It is certainly a wonderful and unexpected fact,” he says, “ that an accurate knowledge of the distribution of birds and insects should enable us to map out lands and continents which disappeared beneath the ocean long before the earliest traditions of the human race. Wherever the geologist can explore the earth’s surface, he can read much of its past history, and can determine approximately its latest movements above and below the sea level ; but wherever oceans and seas now extend he can do nothing but speculate on the very limited data afforded by the depths of the waters. Here the naturalist steps in and enables him to fill up this great gap in the past history of the earth.”1

It is not only animals of all kinds which are of use in solving

Malay Archipelago, p. 14.

INTRODUCTORY.

problems such as these raised by Dr. Wallace. As a rule, animals advance step by step, and thus steadily occupy new territories in their onward march across solid ground ; botanists have urged that plants generally spread in precisely a similar manner.

Botany certainly took the lead in the science of geographical distribution. I need only mention the names of Humboldt, de Candolle, Heer, and Hooker. The latter’s admission, that no material advance was made towards improving the laws of geographical distribution so long as it was believed that the continents and oceans had experienced no great changes of surface or of climate since the introduction of the existing assemblages of animals and plants, implies that he thoroughly believed in the importance of plants in the questions which here concern us. The great majority of botanists are impressed with the fact that plants wander just as animals do, not by saltatory movements, but by slow progression on land. We hnd therefore in great modern works such as Professor Engler’s “ History of Plant Development in the Northern Hemisphere,” that the geographical distribution of plants is pressed into service to decipher the former mutations of land and water on our Continent, on the lines that I propose to adopt in this work.

Plants are in some respects more valuable than animals for our inquiries, for they are as a rule more affected by climate. 1 he first place, indeed, has generally been assigned to plants as tests of former changes in climate, and our fossil forms have sometimes even been spoken of as thermometers of the past. It is especially in connection with the Glacial period1 and its climate that certain plant remains occurring in glacial deposits have been adduced as evidence of an arctic temperature. When we remember, however, that alpine and arctic plants which are supposed to require a cold temperature can be well grown in a gieenhouse atmosphere, we must recognise that implicit faith cannot be placed even in them.

I would also draw attention to the fact that on our own

1 In employing the term “ Glacial” in this connection, I do not intend to convey that I adhere to the general opinion as to the severity of climate prevalent during the geological period referred to.

EUROPEAN ANIMALS.

shores plants of a sub-tropical nature can be grown in the open air almost side by side with arctic plants.

The mountain avens {Dryas octopetala) (Fig. 2) grows wild from

Pig. 2.— The Mountain Avens (Dryas octopetala).

sea level, in Ireland, up to considerable heights. Though abundant in that country it is such a typically arctic species that its occurrence in a fossil condition has often been held to denote that the deposit in which it occurs has been laid down during

INTRODUCTORY.

ii

.an arctic climate. Yet the Irish climate, especially along the west coast, is so mild that some plants of a sub-tropical nature, such as the New Zealand tree fern, can be successfully reared in sheltered spots in. the open.

I only mention these facts in order to show that too much reliance is apt to be placed on the importance of fossil plants as tests of climate.

As for animals and their dependence upon climatic conditions, I might give as an instance the Asiatic tiger (Felis tigris). It is an animal which we usually connect with a tropical climate, and which has yet adapted itself to the most arctic temperature known, as it inhabits both Siberia and India.

After these preliminary remarks, I propose to dwell a little while upon the writings of those who have given the subject of our own fauna and its geological history some attention.

I am commencing with the British and Irish fauna, that is to say, with the fauna of the British Islands, because it discloses, as it were, the key to the larger general European problem.

The first essay which has been published on the origin of the existing fauna of the British Isles was a very remarkable one. It was written in the year 1846 by the late Professor Edward Forbes, and well deserves the name of a classic. The author’s studies led him to believe that the great mass of the animals and plants inhabiting our area had come from the neighbouring continent previous to the isolation of the islands. As regards the plants, Professor Forbes stated that “ the vegetation of the British Islands presents a union of five well-marked floras, four of which are restricted to definite provinces, whilst the fifth, besides exclusively claiming a great part of the area, tends to overspread and commingle with the others.”1