Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/68

 We now come to the third form, Myanthus barbatus (Fig. XXVIII., B), often borne on the same plant with the two preceding forms. Its flowers, in external appearance, but not in essential structure, is the most different of all three. It generally stands in a reversed position, compared with Catasetum and Monachanthus, that is, with the labellum downwards. The labellum is fringed in an extraordinary manner with long papillæ; it has a quite insignificant medial cavity, at the hinder margin of which a curious curved and flattened horn projects. The other petals and sepals are spotted and elongated, with the two lower sepals alone reflexed. The antennæ are not so long as in the male C. tridentatum, and they project symmetrically on each side of the horn-like projection at the base of the labellum, with their tips, which are not toughened with papillæ, almost entering the medial cavity. The stigmatic chamber is of nearly intermediate size between that of the male and female forms: it is lined with utriculi charged with brown matter. The straight and well-firrowed ovarium is nearly twice as long as in Monachanthus, but it is not so thick where it joins the flower; the ovules are not so numerous as in the female form, but are opaque and pulpy after having been kept in spirits, and resemble them in all respects. I believe, but dare not, as in the case of the Monachanthus, speak positively, that I saw the nucleus projecting from the testa. The pollinia are about a quarter of the size of those of the male Catasetum, but have a perfectly well developed disc and pedicel. The pollen-masses were lost in the specimens examined by me; but fortunately Mr. Reiss has given, in the Linnæan Transactions, a drawing of them, showing that they are due proportional size and have the proper folded or cleft structure: so that there can hardly be a doubt that they were functionally perfect. As we thus see that both male and female organs are apparently perfect, Myanthus barbatus may be considered as the hermaphrodite form of the same species, of which the Catasetum is the male and Monachanthus the female.

It is not a little singular that the hermaphrodite Myanthus should resemble in its whole structure much more closely the male form of two distinct species (namely, C. saccatum, and more especially C. callosum) than either its own male or female form.

Finally, the genus Catasetum is interesting in an unusual degree in several respects. The separation of the sexes is unknown in other Orchids, excepting as we shall see probably in the allied genus Cycnoches and in the before-given case of Acropera. In Catasetum we have three sexual forms, generally borne on separate plants, but sometimes mingled together; and these three forms are wonderfully different from each other, much more different than, for instance, a peacock is from a peahen. But the appearance of these three forms on the same plant now ceases to be an anomaly, and can no longer be viewed as an unparalleled instance of variability.

Still more interesting is this genus in its mechanism for fertilisation. We see a flower patiently waiting with its antennæ stretched forth in a well-adapted position, ready to give notice whenever an insects puts its head into the cavity of the labellum. The female Monachanthus, not having pollinia to eject, is destitute of antennæ. In the male and hermaphrodite forms, namely Catasetum tridentatum and Myanthus, the pollinia lie doubled up, like a spring, ready to be instantaneously shot forth when the antennae are touched; the disc end is always projected foremost, and is coated with viscid matter which quickly sets hard and firmly affixes the hinged pedicel to the insect's body. The insect flies from flower to flower, till at last it visits a female or hermaphrodite plant: it then inserts one of the masses of pollen into the stigmatic cavity. When the insect flies away the elastic caudicle, made weak enough to yield to the viscidity of the stigmatic surface, breaks, and leaves behind the pollen-mass; then the pollen-tubes slowly protrude, penetrate the stigmatic canal, and the act of fertilisation is completed. Who would have been bold enough to have surmised that the propagation of a species should have depended on so complex, so apparently artificial, and yet so admirable an arrangement?

I have seen two other genera belonging to the sub-family of Catasetidæ, namely Mormodes and Cycnoches; but the latter arrived in a broken condition.

Mormodes ignea To show how difficult it sometimes is to understand the manner of fertilisation of Orchids, I may state that I had carefully examined twelve flowers, trying various experiments and recording the results, before I could at all make out the meaning and action of the several parts. It was plain that the pollinia were ejected, as in Catasetum, but how each part of the flower played its proper part I could not even conjecture. I had given up the case as hopeless, until, summing up my observations, the explanation presently to be given, and subsequently proved by repeated experiments to be correct, suddenly occurred to me.