Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/87

 chlorantha!

These compound grains are tied together by elastic threads, or are cemented together into so-called waxy masses by some unknown substance. The waxy masses thus found are numerous in the Ophreæ; and graduate in the Epidendreæ and Vandeæ from eight, to four, to two, and, by the cohesion of the two, into a single mass. In the Epidendrea we have both kinds of pollen within the same anther, namely, waxy masses, and caudicles consisting of elastic threads, with numerous compound grains adhering to them.

I can throw no light on the nature of the cohesion of the pollen in these waxy masses; when they are placed in water for three or four days, the compound grains readily fall apart; but the granules forming each grain still firmly cohere, so that the nature of the cohesion in the two cases is different. The elastic threads by which the packets of pollen are tied together in the Ophrea, and which run far up inside the waxy masses of the Vandeæ, are also of a different nature; for they are acted on by chloroform, and by long immersion in spirits of wine; but these fluids have no particular action on the cohesion of the waxy masses. In several Epidendreæ and Vandeæ the exterior pollen-grains of these masses differ from the interior grains, in being larger, and in having yellower and much thicker walls. So that in the contents of a single anther-cell we see a surprising degree of differentiation of structure in the pollen, namely, granules cohering by fours, apparently due to their manner of early development, and the compound grains partly tied together by threads and partly cemented together, with the exterior grains different from the interior grains.

In the Vandeæ, the caudicle, composed of fine coherent threads, is developed from the semi-fluid contents of a layer of cellular membrane. As I find that chloroform has a peculiar and energetic action on the caudicles of all Orchids, and likewise on the glutinous matter enveloping the pollen-grains in Cypripedium, and which can easily be drawn out into threads, one may suspect that in this simpler Orchid we see the primordial condition of the elastic threads by which the pollen-grains in so many other more highly-developed Orchids are tied together.

The caudicle, when largely developed and destitute of pollen-grains, is the most striking peculiarity of the pollinia. In some Neotteæ, especially in Goodyera, we see it in a nascent condition, projecting just beyond the pollen-mass, with the threads only partially confluent. By tracing in the Vandee the gradation from the ordinary naked condition of the caudicle, through Lycaste in which it is almost naked, through Calanthe, to Cymbidium giganteum, in which it is covered with pollen-grains, it seems probably that its ordinary condition has been arrived at by the modification of a pollinium like that of one of the Epidendreæ; namely, by the abortion of the pollen-grains which primordially adhered to separate elastic threads, and by the cohesion of these threads.

In the Ophreæ we have better evidence than that offered by mere gradation, that the long, rigid and naked caudicle has been thus partly formed. I had often observed a cloudy appearance in the middle of the translucent caudicle; and on carefully opening that of Orchis pyramidalis, I found in several specimens in the centre, fully half-way down between the packets of pollen and the viscid disc, several pollen-grains (consisting, as usual, of four united granules), lying quite loose. These grains, from their embedded position, could never by any possibility have been left on the stigma of a flower, and were absolutely useless. Those who can persuade themselves that purposeless organs have been specially created, will think little of this fact. Those, on the contrary, who believe in the slow modification of organic beings, will feel no surprise that the process of change should not always have been perfectly efficient,—that, during and after the many inherited stages of the abortion of the lower pollen-grains and of the coherence of the elastic threads, there should still exist a tendency to the production of a few pollen-grains where they were formerly developed, and that these should consequently be left entangled within the now coherent threads of the caudicle. They will look at the little clouds formed by the loose pollen-grains within the caudicles of Orchis pyramidalis, as good evidence that the pollen-masses of its parent-form was originally like that of Epipactis or Goodyera,