Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/72

 We have seen that when the pollinium is freely ejected upwards it adheres by the whole viscid surface of the disc to any object projecting beyond the edge of the labellum directly over the column. When thus attached, it forms an irregular hoop, with the tom-off anther-case still covering the pollen-masses and lying in close contact with the disc, but protected from adhering to it by the curtain. Whilst in this position the projecting and bowed pedicel would effectually prevent the pollen-masses from being placed on the stigma of a flower, even supposing the anther-case to have fallen off. Now let us suppose the pollinium to be attached to an insect's head, and observe what takes place. The pedicel when first separated by the act of ejection from the rostellum is quite wet on its inferior surface: as this surface dries, the pedicel slowly straightens itself, and when perfectly straight the anther-case readily drops off. The pollen-masses are now naked, and they are attached by easily ruptured caudicles to the end of the pedicel, at the right distance and on that surface which would naturally be placed in contact with the viscid stigma when the insect visited another flower, so that every detail of structure is now perfectly well adapted for the act of fertilisation.

When the anther-case drops off, it has performed its triple function; namely, its hinge as an organ of sense, its weak attachment to the column as a guide causing the pollinium to be at first swung perpendicularly upwards, and its lower margin, together with the curtain of the disc, as a protection to the pollen-masses from being permanently glued to the viscid disc.

From observations made on fifteen flowers, the straightening of the pedicel takes from about twelve to fifteen minutes. The first movement causing the act of ejection is due to elasticity; the second slow movement, which counteracts the first, is due to the drying of the outer and convex surface; but this movement differs from that observed in the pollinia of so many Vandeae and Ophreae, for, when the pollinium of this Mormodes is placed in water, it does not recover the hoop-like form which it had acquired by elasticity.

Mormodes ignea is an hermaphrodite. The pollinia are well developed. The curiously elongated stigmatic surface is extremely viscid and abounds with innumerable utriculi, the contents of which shrink and become coagulated after immersion for less than an hour in spirits of wine. When placed in spirits for a day, the utriculi are so acted on that they disappear, and this I have noticed in no other Orchid. The ovules, after exposure to spirits for a day or two, present the usual semi-opaque, pulpy appearance common to all hermaphrodite and female Orchids. From the unusual length of the stigmatic surface I expected that, if the pollinia were not ejected from the excitement of a touch, the anther-case would detach itself, and that the pollen-masses would swing downwards and fertilise their own flower. Accordingly, I left four flowers untouched; after remaining expanded from eight to ten days, the elasticity of the pedicel conquered the force of attachment and the pollinia were spontaneously ejected, but they were always wasted.

Although Mormodes ignea is an hermaphrodite, yet it must be, in fact, as truly dicious as Catasetum as far as the concurrence of two individuals is concerned in the act of reproduction; for, as it takes from twelve to fifteen minutes, after the act of ejection, before the pedicel of the pollinium straightens itself and the anther-case drops off, it is almost certain that an insect with the pollinium attached to its head would within this time leave one plant and fly to another.

A second species of Mormodes, sent me, unnamed, by Mr. Veitch, is very different from M. ignea both in general appearance and in structure. The yellow petals and sepals are reflexed; the thick labellum is singularly shaped, with its upper surface convex, like a shallow basin turned upside down. The thin column is of extraordinary length, and arches over the labellum. The appearance of the flower is like that of Cycnoches represented on the cover of this volume; but the column in the drawing is too much foreshortened.

The specimens unfortunately arrived broken; but some large flower-buds, of which a section is here given, show the essential structure. We see the elastic pedicel of the pollinium bowed as in the last species; but at the period of growth here represented, the pedicel was still united to the rostellum, the future line of separation being shown by a layer of hyaline tissue, indistinct towards the upper end of the disc. The disc is of gigantic size, and its lower end is produced into a great fringed curtain, which hangs in front of the stigmatic chamber. The adhesion of this disc, when mature, to any object is surprisingly strong. The margins of the stigmatic chamber on each side are slightly protuberant; and these protuberances, like the antennæ in Catasetum, are continuous with the rostellum. The anther is widely different in shape from that in the last species and in Catasetum, and apparently would retain the pollen-masses with more force.