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’ 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 
—“T got not a fact or idea from it®.” 
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®, 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>”, 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 anda 
1 Lamarck, Philosophie zoologique, pp. 223—227. Paris, 1809. 
2 Life and Letters, Vol. 11. 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. x1. p. 242. 
5 Ibid, u. p. 260. See also Origin of Species (6th edit.), p. 6. 
