Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/307

. IX. uses of the variously shaped and placed petals and sepals have been given. So again, the importance of as light difference in the shape of the caudicle of the pollinium of the Bee Ophrys, compared with that of the other species of the same genus, has likewise been referred to; to this might be added the doubly-bent caudicle of the Fly Ophrys. Indeed, the important relation of the length and shape of the caudicle, with reference to the position of the stigma, might be cited throughout many whole tribes. The solid projecting knob of the anther in Epipactis palustris, which does not include pollen, liberates the pollen-masses when it is moved by insects. In Cephalanthera grandiflora, the upright position of the almost closed flower protects the slightly coherent pillars of pollen from disturbance. The length and elasticity of the filament of the anther in certain species of Dendrobium apparently serves for self-fertilisation, if insects fail to transport the pollen-masses. The slight forward inclination of the crest of the rostellum in Listera prevents the anther-case being caught as soon as the viscid matter is ejected. The elasticity of the lip of the rostellum in Orchis causes it to spring up again when only one of the pollen-masses has been removed, thus keeping the second viscid disc ready for action, which otherwise would be wasted. No one who had not studied Orchids would have suspected that these and very many other small details of structure were of the highest importance to each species; and that consequently, if the species were exposed to new conditions of life, and the structure of the several parts varied ever so little, the smallest details of structure might readily be acquired through natural selection. These cases afford a good lesson of caution with respect to the importance of apparently trifling particulars of structure in other organic beings.