The Various Contrivances by which Orchids are Fertilised by Insects/Chapter 5

From Wikisource
Jump to navigation Jump to search


Malaxis paludosa—Masdevallia, curious closed flowers—Bolbophyllum, labellum kept in constant movement by every breath of air—Dendrobium, contrivance for self-fertilisation—Cattleya, simple manner of fertilisation—Epidendrum—Self-fertile Epidendreæ.

I have now described the manner of fertilisation of fifteen genera, found in Britain, which belong, according to Lindley's classification, to the Ophreæ, Arethuseæ, and Neotteæ. A brief account of several foreign genera belonging to these same tribes has been added, from observations published since the appearance of the first edition of this book. We will now turn to the great exotic tribes of the Malaxeæ, Epidendreæ, and Vandeæ, which ornament in so wonderful a manner the tropical forests. My chief object in examining these latter forms has been to ascertain whether their flowers were as a general rule fertilised by pollen brought by insects from another plant. I also wished to learn whether the pollinia underwent those curious movements of depression by which, as I had discovered, they are placed, after being removed by insects, in the proper position for striking the stigmatic surface.

By the kindness of many friends and strangers I have been enabled to examine fresh flowers of several species, belonging to at least fifty exotic genera, in the several sub-tribes of the above three great tribes.[1] It is not my intention to describe the means of fertilisation in all these genera, but merely to select a few curious cases which illustrate the foregoing descriptions. The diversity of the contrivances adapted to favour the intercrossing of flowers, seems to be exhaustless.


Malaxis paludosa.-This rare orchid[2] is the sole representative of the tribe in this country, and it is the smallest of all the British species. The labellum is turned upwards,[3] instead of downwards, so that it does not afford a landing-place for insects as in most other Orchids. Its lower margin clasps the column, making the entrance into the flower tubular. From

Fig. 19.

Darwin - The various contrivances by which orchids are fertilized by insects (1877) - Fig 19.png

Malaxis paludosa.

(Partly copied from Bauer, but modified from living specimens.)

cla. anther. clv. spiral vessels.
clp. pollen. clr. rostellum.
cl. clinandrum. cls. stigma.
cll. labellum.
clu. the sepal which in most orchids stands on the upper side of the flower.
A. Perfect flower viewed laterally, with the labellum in its natural position, upwards.
B. Column viewed in front, showing the rostellum, the pocket-like stigma, and the anterior lateral portions of the clinandrum.
C. Back view of the column in a flower-bud, showing the anther with the included pear-shaped pollinia dimly seen, and the posterior edges of the clinandrum.
D. Back view of an expanded flower, with the anther now contracted and shrivelled, exposing the pollinia.
E. The two pollinia attached to a little transverse mass of viscid matter, hardened by spirits of wine.

its position it partially protects the organs of fructification (fig. 19). In most of the Orchideæ, the upper sepal and the two upper petals afford protection; but here these two petals and all the sepals are reflexed (as may be seen in the drawing, fig. A), apparently to allow insects freely to visit the flower. The position of the labellum is the more remarkable, because it has been purposely acquired, as shown by the ovarium being spirally twisted. In all Orchids the labellum is properly directed upwards, but assumes its usual position on the lower side of the flower by the twisting of the ovarium; but in Malaxis the twisting has been carried so far that the flower occupies the position which it would have held if the ovarium had not been at all twisted, and which the ripe ovarium afterwards assumes, by a process of gradual untwisting.

When the minute flower is dissected, the column is seen to be longitudinally tripartite; the middle portion of the upper half (see fig. B) is the rostellum. The upper edge of the lower part of the column projects where united to the base of the rostellum, and forms a rather deep fold. This fold is the stigmatic cavity, and may be compared to a waistcoat-pocket. I found pollen-masses which had their broad ends pushed by insects into this pocket; and a bundle of pollen-tubes had here penetrated the stigmatic tissue.

The rostellum, which stands immediately above the stigmatic cavity, is a tall-membranous projection of a whitish colour, formed of square cells, and is covered with a thin layer of viscid matter: it is slightly concave posteriorly, and its crest is surmounted by a minute tongue-shaped mass of viscid matter. The column, with its narrow pocket-like stigma and the rostellum above, is united on each side behind to a green membranous expansion, convex exteriorly and concave interiorly, of which the summits on each side are pointed and stand a little above the crest of the rostellum. These two membranes sweep round (see back views, figs. C and D), and are united to the filament or base of the anther; they thus form a cup-like clinandrum behind the rostellum. The use of this cup is to protect laterally the pollen-masses. When I have to treat of the homologies of the different parts, it will be shown by the course of the spiral vessels that these two membranes consist of the two upper anthers of the inner whorl, in a rudimentary condition, but utilised for this special purpose.

In a flower before it expands, a little mass or drop of viscid fluid maybe seen on the crest of the rostellum, rather overhanging its front surface. After the flower has remained open for a little time, this drop shrinks and becomes more viscid. Its chemical nature is different from that of the viscid matter in most Orchids, for it remains fluid for many days, though fully exposed to the air. From these facts I concluded that the viscid fluid exuded from the crest of the rostellum; but fortunately I examined a closely-allied Indian form, namely, the Microstylis rhedii (sent me from Kew by Dr. Hooker), and in this, before the flower opened, there was a similar drop of viscid matter; but on opening a still younger bud, I found a minute, regular, tongue-shaped projection on the crest of the rostellum, formed of cells, which when slightly disturbed resolved themselves into a drop of viscid matter. At this age, also, the front surface of the whole rostellum, between its crest and the pocket-like stigma, was coated with cells filled with similar brown viscid matter; so that there can be little doubt, had I examined a young enough bud of Malaxis, I should have found a similar minute tongue-shaped cellular projection on the crest of the rostellum.

The anther opens widely whilst the flower is in bud, and then shrivels and contracts downwards, so that, when the flower is fully expanded, the pollinia are quite naked, with the exception of their broad lower ends, which rest in two little cups formed by the shrivelled anther-cells. This contraction of the anther is represented in fig. D in comparison with fig. C, which shows the state of the anther in a bud. The upper and much pointed ends of the polliniæ rest on, but project beyond, the crest of the rostellum; in the bud they are unattached, but by the time the flower opens they are always caught by the posterior surface of the drop of viscid matter, of which the anterior surface projects slightly beyond the face of the rostellum. That they are caught without any mechanical aid I ascertained by allowing some buds to open in my room. In fig. E the pollinia are shown exactly as they appeared (but not quite in their natural position) when removed by a needle from a specimen kept in spirits of wine, in which the irregular little mass of viscid matter had become hardened and adhered firmly to their tips.

The pollinia consist of two pairs of very thin leaves of waxy pollen; and the four leaves are formed of angular compound grains which never separate. As the pollinia are almost loose, being retained merely by the adhesion of their tips to the viscid fluid, and by their bases resting in the shrivelled anther-cells, and as the petals and sepals are much reflexed, the pollinia, when the flower is fully expanded, would have been liable to be blown away or out of their proper position, had it not been for the membranous expansions on each side of the column forming the clinandrum, within which they lie safely.

When an insect inserts its proboscis or head into the narrow space between the upright labellum and the rostellum, it will infallibly touch the little projecting viscid mass, and as soon as it flies away it will withdraw the pollinia. I easily imitated this action by inserting any small object into the tubular flower between the labellum and rostellum. When the insect visits another flower, the very thin pollen-leaves attached parallel to the proboscis, or head, will be forced into the pocket-like stigma with their broad ends foremost. I found pollinia in this position glued to the upper membranous expansion of the rostellum, and with a large number of pollen-tubes penetrating the stigmatic tissue. The use of the thin layer of viscid matter, which coats the surface of the rostellum in this genus and in Microstylis, and which is of no use for the transportal of the pollen from flower to flower, seems to be to keep the leaves of pollen fixed in the narrow stigmatic cavity when their lower ends have been inserted by insects. This fact is rather interesting under a homological point of view, for, as we shall hereafter see, the primordial nature of the viscid matter of the rostellum is that which is common to the stigmatic secretion of most flowers, namely, the retention of the pollen, when placed by any means on its stigma.

The flowers of the Malaxis, though so small and inconspicuous, are highly attractive to insects. This was shown by the pollinia having been removed from all the flowers on the spikes which I examined, excepting from one or two close under the buds. In some old flower-spikes every single pollinium had been carried away. Insects sometimes remove only one of the two pairs. I noticed a flower with all four pollen-leaves still in place, with a single one in the stigmatic cavity; and this must clearly have been brought by some insect. Within the stigmas of many other flowers pollen-leaves were observed. The plant produces plenty of seed; and thirteen of the twenty-one lower flowers on one spike had formed large capsules.

We will now turn to some exotic genera. The pollinia of Pleurothallis frolifera and ligulata (?) have a minute caudicle, and mechanical aid is requisite to force the viscid matter from the under side of the rostellum into the anther, thus to catch the caudicles and remove the pollinia. On the other hand, in our British Malaxis and in Microstylis rhedii from India, the upper surface of the minute tongue-shaped rostellum becomes viscid and adheres to the pollinia without any mechanical aid. This appears likewise to be the case with Stelis racemiflora, but the flowers were not in a good state for examination. I mention this latter flower partly because some insect in the hothouse at Kew had removed most of the pollinia, and had left some of them adhering to the lateral stigmas. These curious little flowers are widely expanded and much exposed; but after a time the three sepals close together with perfect exactness, so that it is scarcely possible to distinguish an old flower from a bud: yet, to my surprise, the closed flowers opened when immersed in water.

The allied Masdevallia fenestrata bears an extraordinary flower. The three sepals instead of closing, as in the case of Stelis after the flower has remained for a time expanded, cohere together and never open. Two minute, lateral, oval windows (hence the name fenestrata), are seated high up the flower opposite each other, and afford the only entrance; but the presence of these two minute windows (fig. 20) shows how necessary it is that insects should visit the flower in this case as in that of most other Orchids. How insects perform the act of fertilisation I have failed to understand. At the bottom of the roomy and dark chamber formed by the closed sepals, the minute column stands, and in front of it is the furrowed labellum, with a highly flexible hinge, and on each side the two upper petals; a little tube being thus formed. When therefore a minute insect enters,Fig. 20.Darwin - The various contrivances by which orchids are fertilized by insects (1877) - Fig 20.pngMasdevallia Fenestrata.

The window on the near side is shown darkly shaded.

n. nectary.
or which is less probable, a larger insect inserts its proboscis through either window, it has to find by the sense of touch the inner tube in order to reach the nectary at the base of the flower. Within the little tube, formed by the column, labellum, and lateral petals, a broad and hinged rostellum projects at right angles, which can easily be upturned. Its under surface is viscid, and this viscid matter soon sets hard and dry. The minute caudicles of the pollinia, projecting out of the anther-case, rest on the base of the upper membranous surface of the rostellum. The stigmatic cavity when mature is not very deep. After cutting away the sepals I vainly endeavoured, by pushing a bristle into the tubular flower, to remove the pollinia, but by the aid of a bent needle, this was effected without much difficulty. The whole structure of the flower seems as if intended to prevent the flower from being easily fertilised; and this proves that we do not understand its structure. Some small insect had entered one of the flowers in the hothouse at Kew, for many eggs were deposited within it, near the base.

Of Bolbophyllum I examined the curious little flowers of four species, which I will not attempt fully to describe. In B. cupreum and coccinum, the upper and lower surfaces of the rostellum resolve themselves into viscid matter, which has to be forced upwards by insects into the anther, so as to secure the pollinia. I effected this easily by passing a needle down the flower, which is rendered tubular by the position of the labellum, and then withdrawing it. In B. rhizophoræ the anther-case moves backwards, when the flower is mature, leaving the two pollen-masses fully exposed, adhering to the upper surface of the rostellum. They are held together by viscid matter, and, judging from the action of a bristle, are always removed together. The stigmatic chamber is very deep with an oval orifice, which exactly fits one of the two pollen-masses. After the flower has remained open for some time, the sides of the oval orifice close in and shut the stigmatic chamber completely,—a fact which I have observed in no other Orchid, and which, I presume, is here related to the much exposed condition of the whole flower. When the two pollinia were attached to a needle or bristle, and were forced against the stigmatic chamber, one of the two glided into the small orifice more readily than could have been anticipated. Nevertheless, it is evident that insects must place themselves on successive visits to the flowers in precisely the same position, so as first to remove the two pollinia, and then force one of them into the stigmatic orifice. The two upper filiform petals would serve as guides to the insect; but the labellum, instead of making the flower tubular, hangs down just like a tongue out of a widely open mouth.

The labellum in all the species which I have seen, more especially in B. rhizophoræ, is remarkable by being joined to the base of the column, by a very narrow, thin, white strap, which is highly elastic and flexible; it is even highly elastic when stretched, like an india-rubber band. When the flowers of this species were blown by a breath of wind the tongue-like labella all oscillated to and fro in a very odd manner. In some species not seen by me, as in B. barbigerum, the labellum is furnished with a beard of fine hairs, and these are said to cause the labellum to be in almost constant motion from the slightest breath of air. What the use can be of this extreme flexibility and liability to movement in the labellum, I cannot conjecture, unless it be to attract the notice of insects, as the flowers of these species are dull-coloured, small, and inconspicuous, instead of being large, brightly-coloured, and conspicuous or odoriferous, as in so many other Orchids. The labella of some of the species are said to be irritable, but I could not detect a trace of this quality in those examined by me. According to Lindley, the labellum of the allied Megaclinium falcatum spontaneously oscillates up and down.

The last genus of the Malaxeæ which I will mention is Dendrobium, of which one at least of the species, namely D. chrysanthum, is interesting, from being apparently contrived to effect its own fertilisation, if an insect, when visiting the flower, should fail to remove the pollen-masses. The rostellum has an upper and a small lower surface composed of membrane; and between these is a thick mass of milky-white matter which can be easily forced out. This white matter is less viscid than is usual; but when exposed to the air a film forms over it in less than half a minute, and it soon sets into a waxy or cheesy substance. The large concave but shallow stigmatic surface is seated beneath the rostellum. The produced anterior lip of the anther (see A) almost entirely covers the upper surface of the rostellum.

Fig. 21.

Darwin - The various contrivances by which orchids are fertilized by insects (1877) - Fig 21.png

Dendrobium chrysanthum.

Aa. anther. As. stigma.
Ar. rostellum. Al. labellum.
An. nectary.
A. Lateral view of flower, with the anther in its proper position, before the ejection of the pollinia. All the sepals and petals are removed except the labellum, which is longitudinally bisected.
B. Outline of column, viewed laterally, after the anther has ejected the pollinia.
C. Front view of column, showing the empty cells of the anther, after it has ejected its pollinia. The anther is represented hanging too low down, and covering more of the stigma than it really does.

The filament of the anther is of considerable length, but is hidden in the side view, A, behind the middle of the anther; in the section, B, it is seen, after it has sprung forward: it is elastic, and presses the anther firmly down on the inclined surface of the clinandrum (see fig. B) which lies behind the rostellum. When the flower is expanded the two pollinia, united into a single mass, lie quite loose on the clinandrum and under the anther-case. The labellum embraces the column, leaving a passage in front. The middle portion of the labellum (as may be seen in fig. A) is thickened, and extends up as far as the top of the stigma. The lowest part of the column is developed into a saucer-like nectary, which secretes honey.

As an insect forces its way into one of these flowers, the labellum, which is elastic, will yield, and the projecting lip of the anther will protect the rostellum from being disturbed; but as soon as the insect retreats, the lip of the anther will be lifted up, and the viscid matter from the rostellum forced into the anther, gluing the pollen-mass to the insect, which will thus be transported to another flower. I easily imitated this action; but as the pollen-masses have no caudicle and lie rather far back within the clinandrum beneath the anther, and as the matter from the rostellum is not highly viscid, they were sometimes left behind.

Owing to the inclination of the base of the clinandrum, and owing to the length and elasticity of the filament, as soon as the anther is lifted up it always springs forward, over the rostellum, and remains hanging there with its lower empty surface (fig. C) suspended over the summit of the stigma. The filament now stretches across the space (see fig. B) which was originally covered by the anther. Several times, having cut off all the petals and labellum, and laid the flower under the microscope, I raised the lip of the anther with a needle, without disturbing the rostellum, and saw the anther assume, with a spring, the position represented sideways in fig. B, and frontways in fig. C. By this springing action the anther scoops the pollinium out of the concave clinandrum, and pitches it up in the air, with exactly the right force so as to fall down on the middle of the viscid stigma, where it adheres.

Under nature, however, the action cannot be as thus described, for the labellum hangs downwards; and to understand what follows, the drawing should be placed in an almost reversed position. If an insect failed to remove the pollinium by means of the viscid matter from the rostellum, the pollinium would first be jerked downwards on to the protuberant surface of the labellum, placed immediately beneath the stigma. But it must be remembered that the labellum is elastic, and that at the same instant that the insect, in the act of leaving the flower, lifts up the lip of the anther, and so causes the pollinium to be shot out, the labellum will rebound back, and striking the pollinium will pitch it upwards, so as to hit the adhesive stigma. Twice I succeeded in effecting this by imitating the retreat of an insect, with the flower held in its natural position; and on opening it, found the pollinium glued to the stigma.

This view of the use of the elastic filament, seeing how complicated the action must be, may appear fanciful; but we have seen so many and such curious adaptations, that I cannot believe the strong elasticity of the filament and the thickening of the middle part of the labellum to be useless points of structure. If the action be as I have described, we can perceive their meaning, for it would be an advantage to the plant that its single large pollen-mass should not be wasted, supposing that it failed to adhere to an insect by means of the viscid matter from the rostellum. This contrivance is not common to all the species of the genus; for in neither D. bigibbum nor D. formosum was the filament of the anther elastic, nor was the middle line of the labellum thickened. In D. tortile the filament is elastic; but as I examined only a single flower, and before I had made out the structure of D. chrysanthum, I cannot say how it acts.

Mr. Anderson states[4] that on one occasion the flowers of his Dendrobium cretaceum did not expand, and yet they produced capsules, one of which he sent me. Almost all the numerous seeds in this capsule contained embryos, thus differing greatly from the cases presently to be given of the self-fertilised seeds from the non-expanded flowers of a Cattleya. Mr. Anderson remarks that Dendrobiums are the sole representatives of the Malaxeæ which, as far as he has seen, spontaneously form capsules. He likewise states that in the immense group of the Vandeæ, hereafter to be described, none of the species under his care, with the exception of some belonging to the sub-division of the Brassidæ and of Sarcanthus parishii, has ever spontaneously produced a capsule.


The Epidendreæ and Malaxeæ are characterised by the pollen-grains cohering into large waxy masses. In the latter of these groups the pollinia are said not to be furnished with caudicles, but this is not universally the case, for they exist in Masdevallia fenestrata and some other species in an efficient condition, although unattached and of minute size. In the Epidendreæ, on the other hand, free or unattached caudicles are always present. For my purpose these two great tribes might have been run together; as the distinction drawn from the presence of caudicles does not always hold good. But difficulties of this nature are frequently encountered in the classification of largely developed or so-called natural groups, in which there has been comparatively little extinction.

I will begin with the genus Cattleya, of which I have examined several species. These are fertilised in a very simple manner, different from that in any British Orchid. The rostellum (r, fig. 22, A, B) is a broad, tongue-shaped projection, which arches slightly over the stigma; the upper surface is formed of smooth membrane; the lower surface together with the central portion (originally a mass of cells) consists of a very thick layer of viscid matter. This viscid mass is hardly separated from the viscid matter thickly coating the stigmatic surface which lies close beneath the rostellum. The projecting upper lip of the anther rests on, and opens close over the base of the upper membranous surface of the tongue-shaped rostellum. The anther is kept closed by a spring, at its point of attachment on the top of the column. The pollinia consist of four (or eight in Cattleya crispa) waxy masses, each furnished (see figs. C and D) with a ribbon-like tail, formed of a bundle of highly elastic threads, to which numerous separate pollen-grains are attached. The pollen therefore consists of two kinds, namely, waxy masses and separate though compound grains (each, as usual, consisting of four) united by elastic threads. This latter kind of pollen is identical with that of Epipactis and other Neotteæ.[5] These tails, with their appended pollen-grains, act as caudicles, and are thus designated, for they serve as the means for the removal of the larger waxy masses from the anther-cells. The tips of the caudicles are generally reflexed, and in the mature flower protrude a little

Fig. 22.

Darwin - The various contrivances by which orchids are fertilized by insects (1877) - Fig 22.png


col.a. anther.
col.b. spring at the top of the column.
colp. pollen-masses.
col.r. rostellum.
col.s. stigma.
col. column.
col.l. labellum.
col.n. nectary.
col.g. ovarium, or germen.
A. Front view of column, with all the sepals and petals removed.
B.Section and lateral view of the flower, with all the sepals and petals removed, except the bisected labellum shown only in outline.
C. Anther viewed on the under side, showing the four caudicles with the four pollen-masses beneath.
D. A single pollinium, viewed laterally, showing the pollen-mass and caudicle.

way out of the anther-case (see fig. A) lying on the base of the upper membranous lip of the rostellum. The labellum enfolds the column, making the flower tubular, and its lower part is produced into a nectary, which penetrates the ovarium.

Now for the action of these parts. If any body of size proportional to that of the tubular flower be forced into it—a dead humble-bee acts very well—the tongue-shaped rostellum is depressed, and the object often gets slightly smeared with viscid matter; but in withdrawing it, the rostellum is upturned, and a surprising quantity of viscid matter is forced over the edges and sides, and at the same time into the lip of the anther, which is also slightly raised by the upturning of the rostellum. Thus the protruding tips of the caudicles are instantly glued to the retreating object, and the pollinia are withdrawn. This hardly ever failed to occur in my repeated trials. A living-bee or other large insect alighting on the fringed edge of the labellum, and scrambling into the flower, would depress the labellum and would be less likely to disturb the rostellum, until it had sucked the nectar and began to retreat. When a dead bee, with the four waxy balls of pollen dangling by their caudicles from its back, is forced into another flower, some or all of them are caught with certainty by the broad, shallow, and highly viscid stigmatic surface, which likewise tears off the grains of pollen from the threads of the caudicles.

That living humble-bees can thus remove the pollinia is certain. Sir W. C. Trevelyan sent to Mr. Smith of the British Museum a Bombus hortorum, which was forwarded to me—caught in his hothouse, where a Cattleya was in flower—with its whole back, between the wings, smeared with dried viscid matter, and with the four pollinia attached to it by their caudicles, ready to be caught by the stigma of any other flower if the bee had entered one.

Those species which I have examined of Lælia, Leptotes, Sophronitis, Barkeria, Phaius, Evelyna, Bletia, Chysis, and Cœlogyne, resemble Cattleya in the caudicles of the pollinia being free, and in the viscid matter from the rostellum not coming into contact with them without mechanical aid, as well as in their general manner of fertilisation. In Cœlogyne cristata the upper lip of the rostellum is much elongated. In Evelyna carivata and Chysis eight balls of waxy pollen are all united to a single caudicle. In Barkeria the labellum, instead of enfolding the column, is pressed against it, and this would effectually compel insects to brush against the rostellum. In Epidendrum we have a slight difference; for the upper surface of the rostellum, instead of permanently remaining membranous, as in the above-named genera, is so tender that by a touch it breaks up, together with the whole lower surface, into a mass of viscid matter. In this case the whole of the rostellum, together with the adherent pollinia, must be removed by insects as they retreat from the flower. I observed in E. glaucum that viscid matter exuded from the upper surface of the rostellum when touched, as happens with Epipactis. In fact it is difficult to say, in these cases, whether the upper surface of the rostellum should be called membrane or viscid matter. With Chysis this matter sets nearly hard and dry in twenty minutes, and quite so in thirty minutes after its removal from the rostellum.

In Epidendrum floribundum there is a rather greater difference: the anterior horns of the clinandrum (i. e. the cup on the summit of the column in which the pollinia lie) approach each other so closely as to adhere to the two sides of the rostellum, which consequently lies in a nick, with the pollinia seated over it; and as, in this species, the upper surface of the rostellum resolves itself into viscid matter, the caudicles of the pollinia become glued to it without any mechanical aid. The pollinia, though thus attached, cannot, of course, be removed from their anther-cells without the aid of insects. In this species it seems possible (though, from the position of parts, not probable) that an insect might drag the pollinia out and leave them on the stigma of the same flower. In all the other species of Epidendrum which I examined, and in all the above-mentioned genera, it is evident that the viscid matter has to be forced upwards into the lip of the anther by a retreating insect, which would thus necessarily carry the pollinia from one flower to the stigma of another.

Nevertheless, self-fertilisation takes place in some Epidendreæ. Dr. Crüger says[6] that "we have in Trinidad three plants belonging to this family (a Schomburgkia, Cattleya, and Epidendron) which rarely open their flowers, and they are invariably found to be impregnated when they do open them. In these cases it is easily seen that the pollen-masses have been acted on by the stigmatic fluid, and that the pollen-tubes descend from the pollen-masses in situ down into the ovarian canal." Mr. Anderson, a skilful cultivator of Orchids in Scotland, also states that several of his Epidendreæ fertilise themselves spontaneously.[7] In the case of Cattleya crispa, the flowers sometimes do not expand properly; nevertheless they produce capsules, one of which he sent to me. It contained an abundance of seeds, but on examination I found that only about one per cent. contained an embryo. Similar seeds were more carefully examined by Mr. Gosse, who found that two per cent. contained an embryo. About twenty-five per cent. of the seeds from a self-fertilised capsule of Lælia cinnabarina, also sent to me by Mr. Anderson, were found to be good. It is therefore doubtful whether the capsules spontaneously self-fertilised in the West Indies, as described by Dr. Crüger, were fully and properly fertilised. Fritz Müller informs me that he has discovered in South Brazil an Epidendrum which bears three pollen-producing anthers, and this is a great anomaly in the order. This species is very imperfectly fertilised by insects; but by means of the two lateral anthers the flowers are regularly self-fertilised. Fritz Müller assigns good reasons for his belief that the appearance of the two additional anthers in this Epidendrum, is a case of reversion to the primitive condition of the whole group.[8]

  1. I am particulary indebted to Dr. Hooker, who on every occasion has given me his invaluable advice, and has never become weary of sending me specimens from the Royal Gardens at Kew.

    Mr. James Veitch, jun., has generously given me many beautiful Orchids, some of which were of especial service. Mr. R. Parker also sent me an extremely valuable series of forms. Lady Dorothy Nevill moat kindly placed her magnificent collection of Orchids at my disposal. Mr. Rucker of West Hill, Wandsworth, sent me repeatedly large spikes of Catasetum, a Mormodes of extreme value and some Dendrobiums. Mr. Rodgers of Sevenoaks has given me interesting information. Mr. Bateman, so well known for his magnificent work on Orchids, sent me a number of interesting forms, including the wonderful Angræcum sesquipedale. I am greatly indebted to Mr. Turnbull of Down for allowing me the free use of his hothouses, and for giving me some interesting Orchids; and to his gardener, Mr. Horwood, for his aid in some of my observations.

    Professor Oliver has kindly assisted me with his large stores of knowledge, and has called my attention to several papers. Lastly, Dr. Lindley has sent me fresh and dried specimens, and has in the kindest manner helped me in various ways.

    To these gentlemen I can only express my cordial thanks for their unwearied and generous kindness.

  2. I am greatly indebted to Mr. Wallis, of Hartfield, in Sussex, for numerous living specimens of this Orchid.
  3. Sir James Smith, I believe, first noticed this fact in the 'English Flora,' vol. iv. p. 47, 1828. Towards the summit of the spike the lower sepal does not depend, as represented in the woodcut (fig. 19, A), but projects nearly at right angles. Nor are the flowers always so completely twisted round as here represented.
  4. Journal of Horticulture,' 1863, pp. 206, 287.
  5. The pollen-masses of Bletia are admirably represented on a large scale in Bauer's drawings, published by Lindley in his 'Illustrations.’
  6. 'Journ. Linn. Soc. Bot.' vol. viii. 1864, p. 131.
  7. 'Journal of Horticulture,' 1863, p. 206 and 287: in the latter paper Mr. Gosse gives an account of his microscopical examination of the self-fertilised seeds.
  8. See also 'Bot. Zeitung,' 1869, p. 226, and 1870, p. 152.