THE ORIGIN OF FLOWERS 195 



carried to the stigma of the female blossom the pollen, which in this 

 case was not dusty but sticky, so that it readily adhered to their 

 bodies. 



The securing of cross-fertilization by the development of her- 

 maphrodite flowers has, however, occurred much more frequently, and 

 we can understand that this method secured the advantageous crossing 

 much more perfectly, for the pollen had necessarily to be carried from 

 blossom to blossom, while, in cases like that of the willow, countless 

 male blossoms might be visited for nectar one after the other before 

 the insect made up its mind to fly to a female blossom of the same 

 species. The beginnings of the modification of the unisexual flowers 

 in this direction may be seen in variations which occur even now, 

 for we not infrequently find, in a male catkin, individual blossoms, 

 which, in addition to the stamens, possess also a pistil with a stigma. 

 (Fig. 50 E shows such an abnormal hermaphrodite flower from a 

 poplar.) 



As soon as hermaphrodite flowers came into existence the 

 struggle to attract insects began in a more intense degree. Every 

 little improvement in this direction would form the starting-point of 

 a process of selection, and would be carried on and increased to the 

 highest possible pitch of perfection. 



It was probably the outer envelopes of the blossoms which first 

 changed their original green into other colours, usually those which 

 contrasted strongly with the green, and thus directed the attention of 

 the insects to the flowers. Variations in the colour of ordinary leaves 

 are always cropping up from time to time, whether it be that the 

 green is transformed into yellow or that the chlorophyll disappears 

 more or less completely and red or blue coloured juices take its place. 

 Many insects can undoubtedly see colour, and are attracted by the 

 size of coloured flowers, as Hermann Miiller found by counting the 

 visits of insects to two nearly related species of mallow, one of which, 

 Malva silvesbris, has very large bright rose-red flowers visible from 

 afar, while the other, Malva rotundifolia, has very inconspicuous 

 small pale-red flowers. To the former there were thirty- one different 

 visitors, to the latter he could only make sure of four. The second 

 species, as is to be expected, depends chiefly on self-fertilization. 



It has recently been disputed from various quarters that insects 

 are attracted by the colours of the flowers, and these objections are 

 based chiefly on experiments with artificial flowers. But when, for 

 instance, Plateau, in the course of such experiments saw bees and 

 butterflies first fly towards the artificial flowers, and then turn away 

 and concern themselves no more about them, that only proves that 



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