1893 ENVIRONMENT ON PLANT STEUCTUEES 357 



could come to the Linnean Society, and criticise my 

 paper which I am going to read : ' On the origin of 

 plant structures by self-adaptation to the environ- 

 ment, exemplified by desert and xerophilous plants.' 



In this and in subsequent letters Mr. Henslow 

 explained the subject-matter of his paper, and as 

 it formed the basis of the correspondence, a brief 

 analysis, furnished by Mr. Henslow in a later letter, 

 is here inserted. 



The object of the paper is to show that the origin 

 of varieties and species — as far as the vegetative 

 organs are concerned — is solely due to climatic 

 causes. For the acquired (somatic) characters be- 

 come more or less hereditary if the same environ- 

 ment be maintained. But plants possess every de- 

 gree in their capacities either of reverting, changing, 

 or of stability. 



The result is that I do not see any necessity for 

 natural selection at all in Nature, for the following 

 reasons. 



Variations are often indefinite in cultivation, 

 especially after several years. Therefore to secure 

 a useful race artificial selection is necessary. On 

 the other hand, variation is definite in Nature, all 

 the seedlings varying in one and the same direc- 

 tion, i.e. towards equilibrium with the environmental 

 forces. Darwin knew of this fact, and you have 

 abundantly described it. But Darwin failed to see 

 that this definite variation in Nature is the rule, 

 and not the exception. Hence, as he admits, natural 



