Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/11

 could hardly fail to uncover the viscid disc and adhere to it. But if this did fail to occur, the elastic lip would rise again and re-cover and keep damp the viscid surface. We see the viscid matter within the rostellum attached to the saddle-shaped disc alone, and surrounded by fluid, so that the viscid matter does not set hard till the disc is withdrawn. Then we have the upper surface of the saddle, with its attached caudicles, also kept damp within the bases of the anther-cells, until withdrawn, when the curious clasping movement instantly commences, causing the pollinia to diverge, followed by the movement of depression, which compounded movements together are exactly fitted to cause the ends of the two pollinia to strike the two stigmatic surfaces. These stigmatic surfaces are sticky enough not to tear off the whole pollinium from the proboscis of the moth, but by rupturing the elastic threads to secure a few packets of pollen, leaving plenty for other flowers.

But let it be observed that, although the moth probably takes a considerable time to suck the nectar of any one flower, yet the movement of depression in the pollinia does not commence (as I know by trial) until the pollinia are fairly withdrawn out of their cells; nor will the movement be completed, and the pollinia be fitted to strike the stigmatic surfaces, until about half a minute has elapsed, which will give ample time for the moth to fly to another plant, and thus effect a union between two distinct individuals. Lastly, we have the wonderful growth of the pollen-tubes and their penetration of the stigma, as well as the mysteries of germination, though these are common to all phanerogamic plants. Orchis ustulata resembles O. pyramidalis in some important respects, and differs in others. The labellum is deeply channelled; this channel, which replaces the guiding ridges of O. pyramidalis, leads to the small triangular orifice of the short nectary.

The upper angle of the triangle is overhung by the rostellum, the pouch of which is rather pointed below. Owing to this position of the rostellum, close to the mouth of the nectary, the stigma is necessarily double and lateral; but we here have an interesting gradation, showing how easily the single and slightly lobed medial stigma of O. maculata would pass through the bilobed stigma of O. mascula into that of O. ustulata, and thence into the truly double stigma of O. pyramidalis; for in O. ustulata, directly under the rostellum, there is a narrow rim, in direct continuity with the two lateral stigmas, and which itself has the character of a true stigma, as it is formed of utriculi, or true stigmatic tissue, exactly like that of the lateral stigmas. The viscid discs are somewhat elongated. The pollinia undergo the usual movement of depression, and in acquiring this position the two diverge slightly, so as to be ready to strike the lateral stigmas.

The divergence seemed due to the manner or direction in which the membrane forming the top of the disc contracted obliquely; but I am not sure of this observation.

I have now described the structure, as seen in fresh specimens, of most of the British species of the genus Orchis. All these species absolutely require the aid of insects for their fertilisation. This is obvious from the fact that the pollinia are so closely embedded in their anther-cells, and the disc with its ball of viscid matter in the pouch-formed rostellum, that they cannot be shaken out by violence. We have also seen numerous contrivances by which the pollinia assume, after an interval of time, a position adapted to strike the stigmatic surface; and this indicates that the pollinia are habitually carried from one flower to another. But to prove that insects are necessary I covered up a plant of Orchis morio under a bell-glass, before any of its pollinia had been removed, leaving three adjoining plants uncovered; I looked at the latter every morning, and daily found some of the pollinia removed, till all were removed with the exception of the pollinia in one flower low down on one spike, and with the exception of those in one or two flowers at the apex of each spike, which were never removed. I then looked at the perfectly healthy plant under the bell-glass, and it had, of course, all its pollinia in their cells. I tried an analogous experiment with specimens of O. mascula with exactly the same result. It deserves notice that the spikes which had been covered up, when subsequently left uncovered, had not their pollinia removed, and did not, of course, set any seed, whereas the adjoining plants produced plenty of seed; and from this fact I infer that probably there is a proper season for each kind of Orchis, and that insects cease their visits after the proper season has passed, and the regular secretion of nectar has ceased.

I have been in the habit for twenty years of watching Orchids, and have never seen an insect visit a flower, excepting butterflies twice sucking O. pyramidalis and Gymnadenia conopsea. That bees sometimes visit Orchids I have evidence in a humble and hive bee sent me by Professor Westwood, with pollinia attached to them; and Mr. F. Bond informs me that he has seen pollinia attached to other species of bees; but I feel