IN THE THEOKY OF NATURAL SELECTION. 309 



chance, that they are not the mere sport, of nature, and that they 

 are not made for the enjoyment of man, but that their purpose 

 is to attract insects for the performance of cross-fertilization. It 

 is also well known that this discovery which was made at the 

 end of the last century, and which caused much excitement at that 

 time was completely forgotten, and was brought to light again by 

 Charles Darwin when attacking the same problem. 



In his work entitled 'The Solution of Nature's Secret in the 

 Structure and Fertilization of Flowers ' (' Das entdeckte Geheimniss 

 der Natur im Bau und der Befruchtung der Blumen'), published at 

 Berlin, in 1793, Sprengel showed, in several hundred cases, that the 

 peculiarities in the structure and colours of flowers were calculated 

 to attract insects, and to ensure the fertilization of the flowers by 

 their instrumentality. But it was due to his successor in this line 

 of investigation that the whole significance of the cross-fertilization 

 effected by insects was made clear. Darwin l showed that in many 

 cases, although not in all, the intention of nature was to avoid 

 self-fertilization, and he showed that stronger and more numerous 

 descendants are produced after cross-fertilization. 



After Darwin, several investigators, such as Kerner, Delpino 

 and Hildebrand, have paid further attention to the subject, but it 

 has been especially studied in a most thorough manner by Her- 

 mann Miiller 2 . He looked at the subject from more than one point 

 of view, and showed by direct observation the species of insects 

 which effect cross-fertilization in various species of our native 

 flowers : he also studied the structure of insects in relation to 

 that of flowers, and attempted to establish the mutual adapta- 

 tions which exist between them. In this way he succeeded in 

 throwing much light upon the process of transformation in many 

 species of flowers, and in proving that certain insects, although un- 

 consciously, are, as it were, breeders of certain forms of flowers. He 

 not only distinguished the disagreeably smelling, generally in- 

 conspicuous flowers (' Ekelblumen ') produced by Diptera which live 

 on putrid substances, and the flowers which are produced by butter- 

 flies ; but he also distinguished the flowers bred by saw-flies, by 



1 Ch. Darwin, 'On the fertilization of Orchids by Insects.' London, 1877. 



2 Compare Hermann Miiller, ' Die Befruchtung der Blumen durch Insekten und 

 die gegenseitigen Anpassungen beider.' Leipzig, 1873. See also many articles by the 

 same author in ' Kosmos,' and other periodicals. These later articles are included 

 in the English translation by D'Arcy W. Thompson. 



