No. 507] BOTANICAL SOCIETY OF AMERICA 151 



and to catch a glimpse of the fact that indefinite action, 

 i. e., variation, and definite action of the habitat, i. e., 

 adaptation, were at bottom the same thing. 



His changing view point is recorded in his letters, and 

 hence his later views are not generally known. As a 

 result, scientific opinion has been more or less stereotyped 

 in the well-known statements of the * ' Origin of Species" 

 and has maintained in greater or less degree a position 

 which Darwin himself had forsaken. Darwin's later 

 opinions upon adaptation, as upon the causes of variation, 

 and upon the inheritance of acquired characters, did not 

 differ essentially from those of Lamarck. More im- 

 portant than this, for Lamarck was a prophet, not an in- 

 vestigator, they are in accord with the first results of the 

 application of exact ecological methods to the question 

 of the origin of new forms in natural habitats. 



As far as I am able to judge, after long attending to the subject, the 

 conditions of life appear to act in two ways— directly on the whole 

 organization or on certain parts alone, and indirectly by affecting the 

 reproductive system. 27 



In looking at many small points of differences between species, 

 which, as far as our ignorance permits us to judge, seem quite unim- 

 portant, we must not forget that climate, food, etc., have no doubt 

 produced some direct effect. 28 



In all cases, there are two factors, the nature of the organism, which 

 is much the most important of the two, and the nature of the conditions. 

 The direct action of changed conditions leads to definite or indefinite 

 results. In the latter case, the organization seems to become plastic 

 and we have much fluctuating variability. In the former case, the 

 nature of the organism is such that it yields readily when subjected 

 to certain conditions, and all or nearly all the individuals become 

 modified in the same way. It is very difficult to decide how tar 

 changed conditions, such as climate, food, etc., have acted in a definite 

 manner. There is reason to believe that in the course ofjime the effects 

 have been greater than can be proved by clear evidence. 



The greatest mistake I made was, I now think, I did not attach suffi- 

 cient weight to the direct influence of food, climate, etc., quite inde- 

 pendently of natural selection. When I wrote my book, and tor 

 some years later, I could not find good proof of the direct action {i. e., 

 in producing definite variations) of the environment upon the species. 

 Such proofs are now plentiful. 30 



""Origin," 1: 8. ""Origin," 1: 104. 



