396 Tricotyloiis Races. 



process. As a matter of fact neither one nor the other 

 has occurred. If we would speak of a thoroughhrcd 

 race I only obtained a thoroughbred half race with a 

 mean value of no more than 10 to 15% wdiich remains 

 dependent on the selection of seed-parents with about 

 25%, and is perhaps capable of some very small further 

 improvement. The second hypothesis is so remote from 

 facts that as yet it hardly admits of being tested ; my 

 experiments at any rate, lend no support to it. Rather 

 might they be taken to be in favor of the third view ; 

 for the progress does actually seem to become gradually 

 more rapid after the first few years. But then it should 

 be remembered that selection is at first a ver}^ difficult 

 matter, the tricotyls being still very rare, and for a large 

 part delicate and unfit for further cultivation. In sub- 

 sequent years there are hundreds of tricotyls from which 

 the strongest may be selected ; and we can even limit 

 ourselves to the best specimens produced by the best 

 parents and grandparents, and thus carry out a much 

 more stringent selection. In reality the acceleration of 

 the progress is thus brought about by a practical im- 

 provement in method and not by a biological increase in 

 variability. 



At first I entertained the hope that even if these ex- 

 pectations were not justified some relation between varia- 

 bility and mutability might perhaps exist. ^ I imagined 

 that the capacity for producing mutations might be con- 

 ditioned by external influences and therefore might it- 

 self be a variable character. The diversity amongst the 

 mutation-coefficients of my Oenotheras seemed to sup- 

 ])ort this view.^ Moreover the external conditions which 



* See my Intracellular Pangenesis. 

 "" See Vol. I, p. 337. 



