224 Influence of Environment on Plants 



that potent force in biology which was created by Darwin's Origin 

 of Species (1859). 



The significance of the splendid conception of the transformation 

 of species was first recognised and discussed by Lamarck (1809); as 

 an explanation of transformation he at once seized upon the idea — an 

 intelligible view — that the external world is the determining factor. 

 Lamarck 1 endeavoured, more especially, to demonstrate from the 

 behaviour of plants that changes in environment induce change 

 in form which eventually leads to the production of new species. 

 In the case of animals, Lamarck adopted the teleological view that 

 alterations in the environment first lead to alterations in the needs 

 of the organisms, which, as the result of a kind of conscious effort 

 of will, induce useful modifications and even the development of new 

 organs. His work has not exercised any influence on the progress 

 of science : Darwin himself confessed in regard to Lamarck's work 

 — " I got not a fact or idea from it 2 ." 



On a mass of incomparably richer and more essential data Darwin 

 based his view of the descent of organisms and gained for it general 

 acceptance ; as an explanation of modification he elaborated the 

 ingeniously conceived selection theory. The question of special 

 interest in this connection, namely what is the importance of the 

 influence of the environment, Darwin always answered with some 

 hesitation and caution, indeed with a certain amount of indecision. 



The fundamental principle underlying his theory is that of general 

 variability as a whole, the nature and extent of which, especially in 

 cultivated organisms, are fully dealt with in his well-known book 3 . In 

 regard to the question as to the cause of variability Darwin adopts a 

 consistently mechanical view. He says : "These several considerations 

 alone render it probable that variability of every kind is directly or 

 indirectly caused by changed conditions of life. Or, to put the case 

 under another point of view, if it were possible to expose all the 

 individuals of a species during many generations to absolutely 

 uniform conditions of life, there would be no variability*." Darwin 

 did not draw further conclusions from this general principle. 



Variations produced in organisms by the environment are dis- 

 tinguished by Darwin as "the definite" and "the indefinite 5 ." The 

 first occur "when all or nearly all the offspring of an individual 

 exposed to certain conditions during several generations are modified 

 in the same manner." Indefinite variation is much more general and a 



1 Lamarck, Philosophic zoologique, pp. 223—227. Paris, 1809. 



2 Life and Letters, Vol. n. p. 215. 



3 Darwin, The variation of Animals and Plants under domestication, 2 vols., edit. 1, 

 1868; edit. 2, 1875; popular edit. 1905. 



4 The variation of Animals and Plants (2nd edit.), Vol. n. p. 242. 



5 Ibid. n. p. 260. See also Origin of Species (6th edit.), p. 6. 



