Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/280

260 The caudicle, when largely developed and destitute of pollen-grains, is the most striking of the many peculiarities presented by 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 coherent. In the Vandeæ by tracing 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 probable 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 afterwards by the cohesion of these threads.

In the Ophreae we have better evidence than is afforded by gradation, that their long, rigid and naked caudicles have been developed, at least partially, by the abortion of the greater number of the lower pollen-grains and by the cohesion of the elastic threads by which these grains were tied together. I had often observed a cloudy appearance in the middle of the translucent caudicles in certain species; and on carefully opening several caudicles of Orchis pyramidalis, I found in their centres, fully half-way down between the packets of pollen and the viscid disc, many pollen-grains (consisting, as usual, of four united grains),