22 Mutual Independence of Hereditary Characters 



been sufficiently fixed, and in which, therefore, external 

 influences will still play a prominent part in answering 

 the question as to whether a given seed will produce a 

 true or an atavistic individual. Rimpau and others have 

 taught that with a given kind of seed disturbances and 

 interruptions of growth exercise a powerful influence on 

 the number of specimens that bear seed in the first year. 7 

 And in horticultural and teratological literature one finds 

 scattered numerous data from which the importance of 

 external influences generally is clearly evident. To the 

 experimental investigator there is here opened a large and 

 almost untrodden field. Theoretically the chief task will 

 consist in isolating as much as possible the variations of 

 the hereditary characters in order to obtain, in this way, 

 a knowledge of the individual factors of the respective 

 character. 



The variations which we observe in nature frequently 

 appear to us as if they had suddenly sprung into existence, 

 ancl the same is true of cultures on a small scale, or when 

 the single indivduals are not completely under control. 



However, experience with cultivated plants, during 

 the first years after the beginning of their cultivation, 

 teaches us that the deviations often develop but slowly, 

 and that the modifying influences, as a rule, have to 

 ^operate through several generations before they can ac- 

 cumulate their effect in such a manner that it becomes 

 evident. 8 The facts with reference to this, collected by 

 Darwin, give the impression that the new characters at 

 first arise only in a latent state, and in this condition grad- 



7 Rimpati, A. W. Das Aufschiessen der Runkelruben Land- 

 wirtschaft. Jahrbilcher. 9: 191. 1880. 



8 On this point compare Darwin, The Variation of Animals and 

 Plants under Domestication. Ed. 2. 2: 39. 1875. 



