Let us take another group of beautiful flowers which adorn our greenhouses and our tables: I mean the _Asclepiadæ_, to which the _Stephanotis_ and the _Hoya_ belong. The former is distinguished by the beauty of its scent as well as of its flowers. Both present flowers not merely conspicuous in themselves from their size, form, and colour, but conspicuous also by reason of their grouping. Here, if anywhere, we should expect that beauty should justify itself by its utility. But the facts appear to be just the other way. The pollen is collected together into waxy masses, which are arranged in a very peculiar manner on the pistil; and the pollen tubes pass from the pollen grains whilst still enclosed within the anthers, and so bring about fertilization without the intervention of insect agency. It is difficult to suppose the _Asclepiadæ_ can have become beautiful for the sake of an agency of which they never avail themselves. Our common Fumitory has not very conspicuous flowers, but still they have considerable attractiveness of form and still more of colour, due both to the individual blossom and to their grouping together; and yet _Fumaria_ is said to be self-fertile.[12] A much more brilliantly coloured member of the same family is the _Dicentra (Diclytra) spectabilis_, so familiar in our gardens. Any one who examines the flowers of this species will continually find the pollen grains transferred to the stigma without the slightest trace of the flower ever having opened so as to allow of insect agency. Dr. Lindley[13] has given an account of the mechanism for self-fertilization; and this flower has recently been the subject of an elaborate study by the German botanist, Hildebrand,[14] and he concurs in the view that the anthers inevitably communicate their pollen to the pistil, and that as the result of a very complicated and subtle arrangement of the parts, which it would be useless to attempt to describe without diagrams. But he believes that in addition to the arrangements for self-fertilization, another arrangement exists for producing cross-fertilization by insects; but as the plant has never produced seed under his observation, he is unable to tell whether one mode of fertilization is more useful than the other. I think the evidence of the self-fertilization is far clearer than that of the cross-fertilization.