196 THE EVOLUTION THEORY 



their sight is sharper than we have given them credit for ; for though 

 they may be deceived at a distance, they are not so when they are 

 near ; it is possible, too, that the sense of smell turns the scale \ 

 I have myself made similar experiments with diurnal butterflies, 

 before which I placed a single artificial chrysanthemum midst a mass 

 of natural flowers. It rarely happened indeed that a butterfly settled 

 on the artificial flower ; they usually flew first above it, but did not 

 alight. Twice, however, I saw them alight on the artificial flower, 

 and eagerly grope about with the proboscis for a few moments, then 

 fly quickly away. They had visited the real chrysanthemums or 

 horse-daisies with evident delight, and eagerly sucked up the honey 

 from the many individual florets of every flower, and they now 

 endeavoured to do the same in the artificial flower, and only desisted 

 when the attempt proved unsuccessful. In this experiment the 

 colours were of course only white and yellow ; with red and blue it is 

 probably more difficult to give the exact impression of the natural 

 flower-colours ; and in addition there is the absence of the delicate 

 fragrance exhaled by the flower. 



It must be allowed that the colour is certainly not the sole 

 attraction to the flower; the fragrance helps in most cases, and even 

 this is not the object of the insect's visits. The real object is the 

 nectar, to which colour and fragrance only show the way. The 

 development of fragrance and nectar must, like that of the colour, 

 have been carried on and increased by processes of selection, which 

 had their basis in the necessity for securing insect-visits, and as soon 

 as these main qualities of the flower were established greater refine- 

 ments would begin, and flower-forms would be evolved, which would 

 diverge farther and farther, especially in shape, from the originally 

 simple and regular form of the blossom. 



The reason for this must have lain chiefly in the fact that, after 

 insect- visits in general were secured by a flower, it would be advan- 

 tageous to exclude all insects which would pillage the nectar without 

 rendering in return the service of cross-fertilization — all those, there- 

 fore, which were unsuited either because of their minute size or 

 because of the inconstancy of their visits. Before the butterflies and 

 the bees existed, the regularly formed flat flower with unconcealed 

 nectar would be visited by a mixed company of caddis-flies, saw-flies, 

 and ichneumon-flies. But as the nectar changed its place to the 

 deeper recesses of the flower it was withdrawn from all but the more 

 intelligent insects, and thus the circle of visitors was already narrowed 



1 The experiments of Plateau have since been criticized by Kienitz-Gerloff, who 

 altogether denies their value (1903). 



