Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/67

 sent home by Sir R. Schomburgk. They are here represented (Fig. XXVIII.). The flower of the Monachanthus, like that of the Catasetum, grows lower side uppermost. The labellum is not nearly so deep, especially on the sides, and its edge is crenated. The other petals and sepals are all reflexed, and are not so much spotted as in Catasetum. The bract at the base of the ovarium is much larger. The whole column, especially the filament and the spike-like anther, are much shorter; and the rostellum is much less protuberant. The antenine are entirely absent, and the pollen-masses are rudimentary. These are interesting facts, from corroborating the view taken of the function of the antenine; for as there are no proper pollinia to eject, there could be no use in an organ to convey the stimulus from a touch to the rostellum. I could find no trace of a viscid disc or pedicel; if they exist, they must be extremely rudimentary, for there is hardly any space for the embedment of the disc.

Instead of a large stigmatic chamber, there is a narrow transverse cleft close beneath the small anther. I was able to insert one of the pollen-masses of the male Catasetum into this cleft, which from having been kept in spirits was lined with coagulated beads of viscid matter, and with utriculi. The utriculi, differently from those in Catasetum, were charged (after having been kept in spirits) with brown matter. The ovarium is longer, thicker near the base, and more plainly furrowed than in Catasetum; the ovule-bearing cords are also much longer, and the ovules more opaque and pulpy, as in all common Orchids. I believe that I saw the opening at the partially inverted end of the testa, with a large nucleus projecting; but as the specimens had been kept many years in spirits and were somewhat altered, I dare not speak positively. From these facts alone it is almost certain that Monachanthus is a female plant; and Sir. R. Schomburgk saw it seeding abundantly. Altogether this flower differs in a most remarkable manner from that of the male Catasetum tridentatum, and it is no wonder that they were formerly ranked as distinct genera.

The pollen-masses offer so curious and good an illustration of a structure in a rudimentary condition that they are worth description; but first I must briefly describe the perfect pollen-masses of the male Catasetum. These may be seen at D and E, Fig. XXVI. attached to the pedicel: they consist of a large sheet of cemented or waxy pollen-grains, folded over so as to form a sack, with an open slit (E) along the lower surface, into this slit cellular tissue enters whilst the pollen is in the course of development. Within the lower and produced end of each pollen-mass a layer of highly elastic tissue, forming the caudicle, is attached; the other end being attached to the pedicel of the rostellum. The exterior grains of pollen are more angular, have ticker walls, and are yellower than the interior grains. In the early bud the two pollen-masses are enveloped in two conjoined membranous sacks, which are soon penetrated by the two produced ends of the pollen-masses and by their caudicles; and then the ends of the caudicles adhere to the pedicel. Before the flower expands the membranous sacks including the two pollen-masses open, and leave them resting naked on the back of the rostellum.

In Monachanthus the two membranous sacks containing the rudimentary pollen-masses on the contrary never open; they easily separate from each other and from the anther. The tissue of which they are formed is thick and pulpy. Like most rudimentary parts they vary greatly in size and form. The included and therefore useless pollen-masses are not one-tenth of the bulk of the pollen-masses of the male; they are flask-shaped (p, Fig. XXVIII.), with the lower and produced end greatly exaggerated and almost penetrating through the exterior or membranous sack. The flask is closed, and there is no fissure along the lower surface. The exterior pollen-grains are square and have thicker walls than the interior grains, just as in the proper male pollen; and, what is very curious, each cell has its nucleus. Now, R. Brown has stated that in the early stages of the formation of the pollen-grains in ordinary Orchids a minute areola or nucleus is often visible; so that the rudimentary pollen-grains of the Monachanthus apparently have retained as is so general with rudiments in the animal kingdom an embryonic character. Lastly, at the base, within the flask of pollen, there is a little mass of brown elastic tissue, that is, a vestige of a caudicle, which runs far up the pointed end of the flask, but does not (at least in some of the specimens) come to the surface, and could not have been attached to any part of the rostellum. These rudimentary caudicles are, therefore, utterly useless.

We thus see that every single detail of structure which characterises the male pollen-masses is represented, with some parts exaggerated and some parts slightly modified, by the mere rudiments in the female plant. Such cases are familiar to every observer, but can never be examined without renewed interest. At a period not far distant, naturalists will hear with surprise, perhaps with derision, that grave and learned men formerly maintained that such useless organs were not remnants retained by the principle of inheritance at corresponding periods of early growth, but were specially created and arranged in their proper places like dishes on a table (this is the comparison of a distinguished naturalist) by an Omnipotent hand "to complete the scheme of nature."