The Various Contrivances by which Orchids are Fertilised by Insects

Front matter

THE

VARIOUS CONTRIVANCES

BY WHICH

Preface to the Second Edition

PREFACE

TO

The first edition of this work was published early in the year 1862, and has been for some time out of print. During the two or three years after its appearance I received, through the kindness of various correspondents in different parts of the world, a large number of letters, especially from Fritz Müller in South Brazil, communicating to me many new and curious facts, and calling my attention to some errors. Various memoirs on the fertilisation of orchids have also since been published, and I have myself examined several new and striking forms. A large amount of matter has thus been accumulated; but the present volume would be rendered much too long if the whole were introduced. I have, therefore, selected only the more interesting facts, and have given a brief abstract of the several published papers. The work has thus been remodelled; and the additions and corrections are so numerous that I have found it impossible to follow my usual plan of giving a list of them. I have, however, appended, in chronological order, the titles of all the papers and books on the fertilisation of the Orchideæ which have been published since the appearance of the first edition of the present book. Finally, I will remark that any reader who wishes merely to see how wonderfully complex and perfect are the adaptations for the fertilisation of these plants had better read Chapter VII. on the Catasetidæ. The account of their structure and of the action of the several parts will, I think, be intelligible, if he will first glance at the explanation of the terms given at the close of the Introduction.

List of Papers and Books bearing on the Fertilisation of the Orchideæ

1.7em

Bronn, H. G.—'Charles Darwin, über die Einrichtungen zur Befruchtung britischer und ausländischer Orchideen.' With an Appendix by the Translator on Stanhopea devoniensis. Stuttgart, 1862.

Gray, Asa.—On Platanthera (Habenaria) and Gymnadenia in 'Enumeration of Plants of the Rocky Mountains.'—American Journal of Science and Arts, Second Series, vol. xxxiv., No. 101, Sept. 1862, p. 33.

Gray, Asa.—On Platanthera hookeri, in a review of the first edition of the present work.—American Journal of Science and Arts, vol. xxxiv. July 1862, p. 143.

Anderson, J.—'Fertilisation of Orchids.'—Journal of Horticulture and Cottage Gardener, April 21, 1863, p. 287.

Gosse, P. H.—'Microscopic Observation on some Seeds of Orchids.'—Journal of Horticulture and Cottage Gardener, April 21, 1863, p. 287.

Gray, Asa.—On Platanthera (Habernaria) flava and Gymnadenia tridentata.—American Journal of Science and Arts, vol. xxxvi. Sept. 1863, p. 292.

Journal of Horticulture and Cottage Gardener.—March 17, 1863, p. 206. 'On Orchid Cultivation, Cross-breeding, and Hybridising.'

Scudder, J. H.—On Pogonia ophioglossoides. Proceedings of the Boston Society of Natural History, vol. ix. April, 1863.

Treviranus.—'Ueber Dichogamie nach C. C. Sprengel und Ch. Darwin. § 3. Orchideen.'—Botanische Zeitung, No. 2, 1863, p. 9.

Treviranus.—'Nachträgliche Bemerkungen über die Befruohtung einiger Orchideen.'—Botanische Zeitung, No. 32, 1863, p. 241.

Trimen, R.—'On the Fertilisation of Disa grandiflora, Linn.'—Journal of Linnean Society, Botany, vol. vii. 1863, p. 144.

West of Scotland Horticultural Magazine.—'Fertilisation of Orchids,' Sept. 1863, p. 65.

Ceüger.—'A few Notes on the Fecundation of Orchids, and their Morphology.'—Journal of Linnean Society, Botany, vol. viii. No. 31, 1864, p. 127.

Scott, J.—'On the Individual Sterility and Cross-impregnation of certain Species of Oncidium.'—Journal of Linnean Society, vol. viii. No. 31, 1864, p. 162.

Moggridge, J. Traherne.—'Observations on some Orchids of the South of France.'—Journal of Linnean Society, Botany, vol. viii. No. 32, 1865, p. 256.

Trimen, E.—'On the Structure of Bonatea speciosa, Linn., with reference to its Fertilisation.'—Journal of Linnean Society, vol. ix. 1865, p. 156.

Rohrrach, P.—'Ueber Epipogium gmelini.'—Gekrönte Preisschrift, Göttingen, 1866.

Delpino.—'Sugli Apparecchi della Fecondazione nelle Piante antocarpee.' Florence, 1867.

Hildebrand, F.—'Die Geschlechter-Vertheilung bei den Pflanzen,' &c. Leipzig, 1867, p. 51, et seq.

Hildebrand, F.—'Frederigo Delpino's Beobachtungen über die Bestäubungsvorrichtungen bei den Phanerogamen.'—Botanische Zeitung, No. 34, 1867, p. 265.

Moggridge, J. Traherne, on Ophrys.—'Flora of Mentone,' 1867 (?). Plates 43, 44, 45.

Weale, J. P. Mansel.—'Notes on the Structure and Fertilisation of the Genus Bonatea, with a special description of a Species found at Bedford, South Africa.'—Journal of Linnean Society, Botany, vol. x. 1867, p. 470.

Hildebrand.—'Notizen über die Geschlechtsverhältnisse brasilianischer Pflanzen. Aus einem Briefe von Fritz Müller.' Botanische Zeitung, No. 8, 1868, p. 113.

Müller, Fritz.—'Ueber Befruchtungserscheinungen bei Orchideen.'—Botanische Zeitung, No. 39, 1868, p. 629.

Müller, Hermann.—'Beobachtungen an westfälishen Orchideen.'—Verhandlungen des nat. Vereins für Pr. Rheinl. u. Westf. 1868 and 1869.

Darwin, Charles.—'Notes on the Fertilisation of Orchids.'—Annals and Magazine of Natural History, Sept. 1869.

Delpino.—'Ulteriori Osservazioni sulla Dicogamia nel Regno vegetale.' Parte prima. Milan, 1868–69, pp. 175–78.

Moggridge, J. Traherne.—'Ueber Ophrys insectifera, L. (part).'—Verhandlungen der Kaiserl. Leop. Carol. Akad. (Nova Acta), tom. xxxv. 1869.

Müller, Fritz.—'Ueber einige Befruchtungserscheinungen.'—Botanische Zeitung, No. 14, 1869, p. 224.

Müller, Fritz.—'Umwandlung von Staubgefässen in Stempel bei Begonia. Uebergang von Zwitterblüthigkeit in Getrenntblüthigkeit bei Chamissoa. Triandrische Varietät eines monandrischen Epidendrum.'—Botanische Zeitung, No. 10, 1870, p. 149.

Weale, J. P. Mansel.—'Note on a Species of Disperis found on the Kageberg, South Africa.'—Journal of Linnean Society, Botany, vol. xiii. 1871, p. 42.

Weale, J. P. Mansel.—'Some Observations on the Fertilisation of Disa macrantha.'—Journal of Linnean Society, vol. xiii. 1871, p. 45.

Weale, J. P. Mansel.—' Notes on some Species of Habenaria found in South Africa.'—Journal of Linnean Society, vol. xiii. 1871, p. 47.

Cheeseman, T. F.—'On the Fertilisation of the New Zealand Species of Pterostylis.'—Transactions of the New Zealand Institute, vol. v. 1873, p. 352.

Müller, Hermann.—'Die Befruchtung der Blumen durch Insekten,' &c. Leipzig, 1873, pp. 74–86.

Cheeseman, T. F.—'On the Fertilisation of Acianthus cyrtostilis.'—Transactions of the New Zealand Institute, vol. vii. 1874 (issued 1875), p. 349.

Müller, Hermann.—'Alpine Orchids adapted to Cross-fertilisation by Butterflies.'—Nature, Dec. 31, 1874.

Delpino.—'Ulteriori Osservazioni sulla Dicogamia nel Regno vegetale.' Parte seconda, fasc. ii. Milan, 1875, pp. 149, 150.

Lubbock, Sir J.—'British Wild Flowers.' London, 1875, pp. 162–175.

Fitzgerald, E. D.—'Australian Orchids.' Part I. 1875, Part II. 1876. Sydney, New South Wales.

Introduction

ON THE

FERTILISATION OF ORCHIDS

BY

INSECTS,

&c. &c.

INTRODUCTION.

The object of the following work is to show that the contrivances by which Orchids are fertilised, are as varied and almost as perfect as any of the most beautiful adaptations in the animal kingdom; and, secondly, to show that these contrivances have for their main object the fertilisation of the flowers with pollen brought by insects from a distinct plant. In my volume 'On the Origin of Species' I gave only general reasons for the belief that it is an almost universal law of nature that the higher organic beings require an occasional cross with another individual; or, which is the same thing, that no hermaphrodite fertilises itself for a perpetuity of generations. Having been blamed for propounding this doctrine without giving ample facts, for which I had not sufficient space in that work, I wish here to show that I have not spoken without having gone into details.

I have been led to publish this little treatise separately, as it is too large to be incorporated with any other subject. As Orchids are universally acknowledged to rank amongst the most singular and most modified forms in the vegetable kingdom, I have thought that the facts to be given might lead some observers to look more curiously into the habits of our several native species. An examination of their many beautiful contrivances will exalt the whole vegetable kingdom in most persons' estimation. I fear, however, that the necessary details are too minute and complex for any one who has not a strong taste for Natural History. This treatise affords me also an opportunity of attempting to show that the study of organic beings may be as interesting to an observer who is fully convinced that the structure of each is due to secondary laws, as to one who views every trifling detail of structure as the result of the direct interposition of the Creator.

I must premise that Christian Konrad Sprengel, in his curious and valuable work, 'Das entdeckte Geheimniss der Natur,' published in 1793, gave an excellent outline of the action of the several parts in the genus Orchis; for he well knew the position of the stigma, and he discovered that insects were necessary to remove the pollen-masses. But he overlooked many curious contrivances,—a consequence, apparently, of his belief that the stigma generally receives pollen from the same flower. Sprengel, likewise, has partially described the structure of Epipactis; but in the case of Listera he entirely misunderstood the remarkable phenomena characteristic of that genus, which has been well described by Dr. Hooker in the 'Philosophical Trans- actions' for 1854. Dr. Hooker has given a full and accurate account, with drawings, of the structure of the parts; but from not having attended to the agency of insects, he did not fully understand the object gained. Robert Brown, in his celebrated paper in the 'Linnean Transactions,' expresses his belief that insects are necessary for the fructification of most Orchids; but adds, that the fact of all the capsules on a dense spike not infrequently producing seed, seems hardly reconcilable with this belief: we shall hereafter find that this doubt is groundless. Many other authors have given facts and expressed their belief, more or less fully, on the necessity of insect-agency in the fertilisation of Orchids.

In the course of the following work I shall have the pleasure of expressing my deep obligation to several gentlemen for their unremitting kindness in sending me fresh specimens, without which aid this work would have been impossible. The trouble which several of my kind assistants have taken has been extraordinary: I have never once expressed a wish for aid or for information which has not been granted me, as far as possible, in the most liberal spirit.

EXPLANATION OF TERMS.

In case any one should look at this treatise who has never attended to Botany, it may be convenient to explain the meaning of the common terms used. In most flowers the stamens, or male organs, surround in a ring the one or more female organs, called the pistils. In all common Orchids there is only one well-developed stamen, which is confluent with the pistils, and they form together the column. Ordinary stamens consist of a filament, or supporting thread (rarely seen in British Orchids), which carries the anther; and within the anther lies the pollen or male vivifying element. The anther is divided into two cells, which are very distinct in most Orchids, so much so as to appear in some species like two separate anthers. The pollen in all common plants consists of fine granular powder: but in most Orchids the grains cohere in masses, which are often supported by a very curious appendage, called the caudicle. This part and all the other organs will, hereafter be more fully described and figured under the head of the first species, Orchis mascula. The pollen-masses, with their caudicles and other appendages, are called the pollinia.

Orchids properly have three pistils or female organs, united together, the upper and anterior surfaces of two of which form the two stigmas. But the two are often completely confluent, so as to appear as one. The stigma is penetrated in the act of fertilisation by long tubes, emitted by the pollen-grains, which carry the contents of the grains down to the ovules or young seeds in the ovarium.

The upper stigma is modified into an extraordinary organ, called the rostellum, which in many Orchids presents no resemblance to a true stigma. When mature it either includes or is altogether formed of viscid matter. In many species the pollen-masses are firmly attached to a portion of the exterior membrane, which, when insects visit the flowers, is removed, together with the pollen-masses. This removable portion consists in most British Orchids merely of a small piece of membrane, with a layer or ball of viscid matter underneath, and I shall call it the "viscid disc;" but in many exotic species the portion removed is so large and so important, that one part must be called, as before, the viscid disc, and the other part the pedicel of the rostellum, to the end of which the pollen-masses are attached. Authors hare called that portion of the rostellum which is removed, the "gland" or "retinaculum," from its apparent function of retaining the pollen-masses in their places. The pedicel, or prolongation of the rostellum, to which in many exotic species the pollen-masses are attached, seems generally to have been confounded, under the name of caudicle, with the true caudicle of the pollen-masses, though their nature and origin are totally different. The part of the rostellum which is left after the removal of the discs and viscid matter, is sometimes called the "bursicula," or "fovea," or "pouch." But it will be found convenient to avoid all these terms, and to call the whole modified stigma the rostellum—sometimes adding an adjective to define its shape; that portion of the rostellum which is removed with the pollen-masses being called the viscid disc, together in some cases with the pedicel.

Lastly, the three outer divisions of the flower are called sepals, and form the calyx; but, instead of being green, as in most common flowers, they are generally coloured, like the three inner divisions or petals of the flower. In almost all the species, one of the petals, which is properly the upper one, is larger than the others and stands on the lower side of the flower, where it offers a landing-place for insects, having been carried round by the twisting of the ovarium. It is called the lower lip or labellum, and often assumes most singular shapes. It secretes nectar for the sake of attracting insects, and is often produced into a spur-like nectary.

Chapter 1

OPHREÆ.

1.5em

Throughout the following volume I have followed, as far as I conveniently could, the arrangement of the Orchideæ given by Lindley. The British species belong to five of his tribes, the Ophreæ, Neotteæ, Arethuseæ, Malaxeæ and Cypripedeæ, but the two latter tribes contain each only a single genus. Various British and foreign species belonging to the several tribes are described in the first eight chapters. The eighth also contains a discussion on the homologies of the flowers of the Orchideæ. The ninth chapter is devoted to miscellaneous and general considerations.

The Ophreæ include most of our common British species, and we will begin with the genus Orchis. The reader may find the following details rather difficult to understand; but I can assure him, if he will have patience to make out the first case, the succeeding ones will be easily intelligible. The accompanying diagrams (fig. 1, p. 8) show the relative position of the more important organs in the flower of the Early Orchis (O. mascula). The sepals and the petals have been removed, excepting the labellum with its nectary. The nectary is shown only in the side view (n, fig. A); for its enlarged orifice is almost hidden in shade in the front view (B). The stigma (s) is bilobed, and consists of two almost confluent stigmas; it lies under the pouch-formed rostellum (r). The anther (a, in B and A) consists of two rather widely separated cells, which are longitudinally open in front: each cell includes a pollen-mass or pollinium.

A pollinium removed out of one of the two anther-cells is represented by fig. C; it consists of a number of wedge-formed packets of pollen-grains (see fig. F, in which the packets are forcibly separated), united together by excessively elastic, thin threads. These threads become confluent at the lower end of each pollen-mass, and compose the straight elastic caudicle (c, C). The end of the caudicle is firmly attached to the viscid disc (d, C), which consists (as may be seen in the section of the pouch-formed rostellum, fig. E) of a minute oval piece of membrane, with a ball of viscid matter on its under side. Each pollinium has its separate disc; and the two balls of viscid matter lie enclosed together (fig. D) within the rostellum.

The rostellum is a nearly spherical, somewhat pointed projection (r, figs. A and B) overhanging the two almost confluent stigmas, and must be fully described, as every detail of its structure is full of significance. A section through one of the discs and balls of viscid matter is given (fig. E); and a front view of both viscid dics within the rostellum (fig. D) is likewise given. This latter figure (D) probably best serves to explain the structure of the rostellum; but it must be understood that the front lip is here considerably depressed. The lowest part of the anther is united to the back of the rostellum, as may be seen in fig. B. At an early period of growth the rostellum

.

Orchis mascula

Description of Fig. 1.

|a. anther, consisting of two cells. | |n. nectary.

|r. rostellum. | |p. pollen-mass.

|s. stigma. | |c. caudicle of pollinium.

|l. labellum. | |d. viscid disc of pollinium.

3em

consists of a mass of polygonal cells, full of brownish matter, which cells soon resolve themselves into two balls of extremely viscid semi-fluid matter, void of structure. These viscid masses are slightly elongated, almost flat on the top, and convex below. They lie quite free within the rostellum (being surrounded by fluid), except at the back, where each viscid ball adheres to a small portion or disc of the exterior membrane of the rostellum. The ends of the two caudicles are strongly attached externally to these two little discs of membrane.

The membrane forming the whole exterior surface of the rostellum is at first continuous; but as soon as the flower opens the slightest touch causes it to rupture transversely in a sinuous line, in front of the anther-cells and of the little crest or fold of membrane (see fig. D) between them. This act of rupturing makes no difference in the shape of the rostellum, but converts the front part into a lip, which can be depressed easily. This lip is represented considerably depressed in fig. D, and its edge is seen, fig. B, in the front view. When the lip is thoroughly depressed, the two balls of viscid matter are exposed. Owing to the elasticity of the hinder part, the lip or pouch, after being pressed down, springs up again and encloses the two viscid balls.

I will not affirm that the rupturing of the exterior membrane of the rostellum never takes place spontaneously; and no doubt the membrane is prepared for rupture by having become very weak along defined lines; but several times I saw the act ensue from an excessively slight touch—so slight that I conclude that the action is not simply mechanical, but, for the want of a better term, may be called vital. We shall hereafter meet with other cases, in which the slightest touch or the vapour of chloroform causes the exterior membrane of the rostellum to rupture along certain defined lines.

At the same time that the rostellum becomes transversely ruptured in front, it probably (for it was impossible to ascertain this fact from the position of the parts) ruptures behind in two oval lines, thus separating and freeing from the rest of the exterior surface of the rostellum the two little discs of membrane, to which the two caudicles are attached externally, and to which the two balls of viscid matter adhere internally. The line of rupture is thus very complex, but strictly defined.

As the two anther-cells are open longitudinally in front from top to bottom, even before the flower expands, it follows that as soon as the rostellum is properly ruptured from the effects of a slight touch, its lip can be depressed easily, and, the two little discs of membrane being already separate, the two pollinia now lie absolutely free, but are still embedded in their proper places. So that the packets of pollen and the caudicles still lie within the anther-cells; the discs still form part of the rostellum, but are separate; and the balls of viscid matter still lie concealed within the rostellum.

Now let us see in the case of Orchis mascula (fig. 1) how this complex mechanism acts. Suppose an insect to alight on the labellum, which forms a good landing-place, and to push its head into the chamber (see side view, A, or front view, B), at the back of which lies the stigma (s), in order to reach with its proboscis the end of the nectary; or, which does equally well to show the action, push very gently a sharply-pointed common pencil into the nectary. Owing to the pouch-formed rostellum projecting into the gangway of the nectary, it is scarcely possible that any object can be pushed into it without the rostellum being touched. The exterior membrane of the rostellum then ruptures in the proper lines, and the lip or pouch is easily depressed. When this is effected, one or both of the viscid balls will almost infallibly touch the intruding body. So viscid are these balls that whatever they touch they firmly stick to. Moreover the viscid matter has the peculiar chemical quality of setting, like a cement, hard and dry in a few minutes' time. As the anther-cells are open in front, when the insect withdraws its head, or when the pencil is withdrawn, one pollinium, or both, will be withdrawn, firmly cemented to the object, projecting up like horns, as shown (fig. 2)

.

A. Pollen-mass of O. mascula, when first attached.

B. Pollen-mass of O. mascula, after the act of depression.

by the upper figure, A. The firmness of the attachment of the cement is very necessary, for if the pollinia were to fall sideways or backwards they could never fertilise the flower. From the position in which the two pollinia lie in their cells, they diverge a little when attached to any object. Now suppose that the insect flies to another flower, or let us insert the pencil (A, fig. 2), with the attached pollinium, into the same or into another nectary: by looking at the diagram (fig. 1, A) it will be evident that the firmly attached pollinium will be simply pushed against or into its old position, namely, into the anther-cell. How then can the flower be fertilised? This is effected by a beautiful contrivance: though the viscid surface remains immovably affixed, the apparently insignificant and minute disc of membrane to which the caudicle adheres is endowed with a remarkable power of contraction (as will hereafter be more minutely described), which causes the pollinium to sweep through an angle of about ninety degrees, always in one direction, viz., towards the apex of the proboscis or pencil, in the course of thirty seconds on an average. The position of the pollinium after the movement is shown at B in fig. 2. After this movement, completed in an interval of time which would allow an insect to fly to another plant, it will be seen, by turning to the diagram (fig. 1, A), that, if the pencil be inserted into the nectary, the thick end of the pollinium now exactly strikes the stigmatic surface.

Here again comes into play another pretty adaptation, long ago noticed by Robert Brown. The stigma is very viscid, but not so viscid as when touched by a pollinium to pull the whole off an insect's head or off a pencil, yet sufficiently viscid to break the elastic threads (fig. 1, F) by which the packets of pollen-grains are tied together, and leave some of them on the stigma. Hence a pollinium attached to an insect or to a pencil can be applied to many stigmas, and will fertilise all. I have often seen the pollinia of Orchis pyramidalis adhering to the proboscis of a moth, with the stump-like caudicles alone left, all the packets of pollen having been left glued to the stigmas of the successively visited flowers.

One or two other little points must be noticed. The balls of viscid matter within the pouch-formed rostellum are surrounded with fluid; and this is very important, for, as already mentioned, the viscid matter sets hard when exposed to the air for a very short time. I have pulled the balls out of their pouches, and found that they had entirely lost the power of adhesion after a few minutes. Again, the little discs of membrane, the movement of which, as causing the movement of the pollinia, is so absolutely indispensable for the fertilisation of the flower, lie at the upper and back surface of the rostellum, and are closely enfolded and thus kept damp within the bases of the anther-cells; and this is very necessary, as an exposure of about thirty seconds causes the movement of depression to take place; but as long as the disc is kept damp, the pollinia remain ready for action whenever removed by an insect.

Lastly, as I have shown, the pouch, after being depressed, springs up to its former position; and this is likewise of great service; for if this action did not take place, and an insect after depressing the lip failed to remove the two viscid balls, or if it removed one alone, then in the first case both, and in the second case one would be left exposed to the air; consequently one or both would quickly lose all adhesiveness, and the pollinium would be rendered absolutely useless. That with many kinds of Orchids insects often remove only one of the two pollinia at a time is certain; it is even probable that they generally remove only one, for the lower and older flowers almost always have both pollinia removed, whilst the younger flowers close beneath the buds, which will have been seldomer visited, have frequently only one pollinium removed. In a spike of Orchis maculata, I found as many as ten flowers, chiefly the upper ones, which had only one pollinium removed; the other pollinium being still in its proper place with the lip of the rostellum well closed up; so that all the mechanism was perfect for its subsequent removal by some other insect.

When the first edition of this book was published, I had not seen any insects visiting the flowers of the present species; but a friend watched some plants, and saw them visited by several humble-bees, apparently Bombus muscorum; and Dr. H. Müller has seen four other species of Bombus at work. He caught ninety-seven specimens, and of these thirty-two had pollinia attached to their heads.

The description now given of the action of the organs in Orchis mascula applies to O. morio, fusca, maculata, and latifolia. These species present slight and apparently co-ordinated differences in the length of their caudicles, in the direction of the nectary, in the shape and position of the stigma, but they are not worth detailing. In all, the pollinia when removed from the anther-cells undergo the curious movement of depression, which is so necessary to place them in a right position on an insect's head for striking the stigmatic surface of another flower. Six species of humble-bees, the hive-bee and two other kinds have been seen by H. Müller and myself visiting the flowers of Orchis morio. On some of the hive-bees from ten to sixteen pollen-masses adhered; to the head of Eucera longicornis eleven, to the head of Osmia rufa several, and several to the bare surface close above the mandibles of Bombus muscorum. H. Müller has seen twelve different kinds of bees visiting the flowers of O. latifolia, which are also visited by Diptera. My son George observed for some time plants of O. maculata, and saw many specimens of a fly (Empis livida) inserting their proboscides into the nectary; and subsequently the same fact was observed by me. He brought home six specimens of this Empis, with pollinia attached to their spherical eyes, on a level with the bases of the antennæ. The pollinia had undergone the movement of depression, and stood a little above and parallel to the proboscis: hence they were in a position excellently adapted to strike the stigma. Six pollinia were thus attached to one specimen, and three to another. My son also saw another and smaller species (Empis pennipes) inserting its proboscis into the nectary; but this species did not act so well or so regularly as the other in fertilising the flowers. One specimen of this latter Empis had five pollinia, and a second had three pollinia, attached to the dorsal surface of its convex thorax. H. Müller has seen two other genera of Diptera at work on this orchis, with pollinia attached to the front part of their bodies; and on one occasion he saw a humble-bee visiting the flowers.

We now come to Orchis (sub-genus, Anacamptis) pyramidalis, one of the most highly organised species which I have examined, and which is ranked by several botanists as a distinct genus. The relative position of the parts (fig. 3) is here considerably different from what it is in O. mascula and its allies. There are two quite distinct rounded stigmatic surfaces (s, s, A) placed on each side of the pouch-formed rostellum. This latter organ, instead of standing some height above the nectary, is brought down (see side view B) so as to overhang and partially to close its orifice. The ante-chamber to the nectary, formed by the union of the edges of the labellum to the column, which is large in O. mascula and its allies, is here small. The pouch-formed rostellum is hollowed out on the under side in the middle: it is filled with fluid. The viscid disc is single and of the shape of a saddle (figs. C and E); it carries on its nearly flat top or seat the two caudicles of the pollinia, the ends of which firmly adhere to its upper surface. Before the membrane of the rostellum ruptures, the saddle-formed disc can be clearly seen to be continuous with the rest of the surface. The disc is partially hidden and kept damp (which is of great importance) by the over-folding bases of the two anther-cells. It consists of several layers of minute cells, and is therefore rather thick; it is lined beneath with a layer of highly adhesive matter, which is formed within the rostellum. It corresponds strictly to the two minute, oval, separate discs to which the two caudicles of O. mascula and its allies are attached.