Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/169

CHAPTER VI.

VANDEÆ.

Structure of the column and pollinia—Importance of the elasticity of the pedicel; its power of movement—Elasticity and strength of the caudicles—Calanthe with lateral stigmas, manner of fertilisation—Angræcum sesquipedale, wonderful length of nectary—Species with the entrance into the stigmatic chamber much contracted, so that the pollen-masses can hardly be inserted—Coryanthes, extraordinary manner of fertilisation.

We now come to the immense tribe of the Vandeæ, which includes many of the most magnificent productions of our hothouses, but like the Epidendreæ has no British representative. I have examined twenty-nine genera. The pollen consists of waxy masses, as in the two last tribes, and each ball of pollen is furnished with a caudicle, which becomes, at an early period of growth, united to the rostellum. The caudicle is seldom attached directly to the viscid disc, as in most of the Ophreæ, but to the upper and posterior surface of the rostellum; and this part is removed by insects, together with the disc and pollen-masses. The sectional diagram (fig. 23), with the parts separated, will best explain the type-structure of the Vandeæ. As in the rest of the Orchideæ there are three confluent pistils; of these the dorsal one (2) forms the rostellum arching over the two others (3) which unite to form a single stigma. On the left hand we have the filament (1) bearing the anther. The anther opens at an early period, and the tips of the two caudicles (but only one caudicle and one pollen-mass are re-