It has been remarked that the chapter on the Origin of Flowers in the German Edition contains no discussion and refutation of the objections which have up till recently been urged against the theory of flowers propounded by Darwin and Hermann Müller. I admit that this chapter seemed to be so harmonious and so well rounded, and at the same time so convincing as to the reality of the processes of selection, that the feeble objections to it, and the attempts of opponents to find another explanation of the phenomena, might well be disregarded in this book. However, the most important of these objections and counter-theories may here be briefly mentioned. Plateau in Ghent was the first to collect _facts_ which appeared to contradict the Darwinian theory of flowers; he observed that insects avoided _artificial_ flowers, even when they were indistinguishable in colour from natural ones as far as our eyes could perceive, and he concluded from this that it is not the colour which guides the insects to the flowers, that they find the blossoms less by their sense of sight than by their sense of smell. But great caution is required in drawing conclusions from experiments of this kind. I once placed artificial marguerites (_Chrysanthemum leucanthemum_) among natural ones in a roomy frame in the open air, and for a considerable time I was unable to see any of the numerous butterflies (_Vanessa urticæ_), which were flying about the real chrysanthemums, settle on one of the artificial flowers. The insects often flew quite close to them without paying them the least attention, and I was inclined to conclude that they either perceived the difference at sight, or that they missed the odour of the natural flowers in the artificial ones. But in the course of a few days it happened twice in my presence that a butterfly settled on one of the artificial blooms and _persistently groped about with fully outstretched tube to find the entrance to the honey_. It was only after prolonged futile attempts that it desisted and flew away. That bees are guided by the eye in their visits to flowers has been shown by A. Forel, who cut off the whole proboscis, together with the antennæ, from humble-bees which were swarming eagerly about the flowers. He thus robbed them of the whole apparatus of smell, and nevertheless they flew down from a considerable height direct to the same flowers. An English observer, Mr. G. N. Bulman, has been led to believe, with Plateau, that it is a matter of entire indifference to the bees whether the flowers are blue, or red, or simply green in colour, if only they contain honey, and that therefore the bees could have played no part in the development of blue flowers, as Hermann Müller assumed they had, and that they could have no preference for blue or any other colour, as Sir John Lubbock and others had concluded from their experiments. This is correct in so far that bees feed as eagerly on the greenish blossoms of