n6 BIOMETRY 



gradual return towards the mean character of the 

 original race.* 



It must be remembered that in the calculation which 

 led to this result perfect normal variability was assumed, 

 and the contribution of every ancestor of the same 

 degree to the hereditary endowment of the offspring 

 was supposed to be exactly equal. Since both these 

 assumptions are very unlikely to be realized in any 

 actual case, the statement here given must only be 

 regarded as an approximate indication of what is 

 likely to take place. 



Some remarkable observations have been published 

 by Professor Johannsen, of Copenhagen, and from 

 them are drawn conclusions which seem likely to lead 

 to a distinct advance in our understanding of the pro- 

 cess of so-called continuous variation, and of the way 

 in which such variations are transmitted. Johannsen's 

 conclusions have more recently received remarkable 

 confirmation from the work of Jennings on protozoa, 

 so that we are now justified in accepting the theory 

 of the pure line as a well-established working hypo- 

 thesis. We shall confine our present account to 

 Johannsen's now classical observations. 



The experiments in question were made upon plants 

 which could be self-fertilized for a series of generations. 

 In this way many complications were avoided which 

 are inevitably introduced in the case of biparental 



* From this it seems necessarily to follow that it is impos- 

 sible to establish a permanent breed simply by a process of 

 selection. Professor Pearson, however, avoids this conclusion. 



