238 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



variation has been most carefully studied by statistical 

 methods, Galton and Weldon being the well - known 

 pioneers in this field. 1 In fact, if we are allowed to assume 

 that this sort of variation is the outcome of a variation of 

 conditions in the most general meaning of the word we 

 only follow the opinion which has almost universally 

 been adopted by the biologists 2 that are working at this 

 branch of the subject. Variation proper is now generally 

 allowed to be the consequence of variations in nutrition ; 

 the contingencies of the latter result in contingencies 

 of the former, and the law of contingencies is the same 



for both, being the most general law of probability. Of 



. 



course under such an aspect fluctuating variation could 

 hardly be called an exception, but rather an addition to 

 inheritance. 



But there are other restrictions of our definition of 

 heredity. The initial stage which is formed again by an 

 organism is not always quite identical in itself with the 

 initial stage of its own parent : Bateson and de Vries 

 were the first to study in a systematic way these real ex- 

 ceptions 3 to true inheritance. As you know, de Vries has 

 given them the name of " mutations." What is actually 

 known on this subject is not much at present, but never- 

 theless is of great theoretical value, being the only real 



1 H. M. Vernon, Variations in Animals and Plants, London, 1903. 



2 De Vries, Die Mutationstheorie, i., 1901 ; and Klebs, Jahrb. iviss. Bot. 

 42, 1905. 



3 They would not be "real exceptions" if Klebs (Arch. Entw. Mccli. 24, 

 1907) were right in saying that both variations and mutations owe their 

 existence to external agents. What is really proved by Klebs is the possibility 

 of changing the type of a curve of variation and of provoking certain dis- 

 continuous varieties by external means. See also Blaringhem (Comptes rend. 

 1905-6, and Soc. de Biol. 59, 1905), and MacDougal (Rep. Depart. Bot. Res., 

 5th Year-look Carnegie Inst., Washington, 129). 



