v.] IN THE THEORY OF NATURAL SELECTION. 317 



and the butterfly which fertihzes it, but between these two on 

 the one side, and the other would-be visitors of the flower on 

 the other. Further details as to the advantages which the 

 flower gains by excluding all other visitors, and the butterfly 

 by being the only visitor of the flower, and also as to the 

 manifold and elaborate mutual adaptations between insects and 

 flowers, and as to the advantages and disadvantages which 

 follow from the concealment of the honey — will be found in 

 Hermann Miiller's^ work on the fertilization of flowers, in 

 which all these subjects are minutely discussed, and are clearly 

 explained in a most admirable manner. 



Appendix III. Adaptations in Plants^. 



It is well known that Christian Conrad Sprengel was the first 

 to recognise that the forms and colours of flowers are not due 

 to 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 Ge- 

 heimniss der Natur im Bau und der Befruchtung der Blumen '), 

 published at Berlin, in 1793, Sprengel showed, in several hun- 

 dred 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^ 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. 



^ English Edition, translated by D'Arcy W. Thompson, B.A. London, 

 1883, p. 509 et seqq. 



^ Appendix to page 266. 



3 Ch. Darwin, ' On the Fertilization of Orchids by Insects.' London. 

 1877. 



