GENETICS 161 



If we have here, as I believe, a genuine disruption we can 

 well understand that Mendelian methods of breeding are bound 

 to exhibit a multiplicity of segregations and also of new com- 

 binations. When a complex community, once flourishing and 

 rich in correspondences, starts on the decline, some of the com- 

 ponent parts at least will not break up altogether, but enter 

 into fresh combination with others that have remained 

 tolerably wholesome and sufficiently sympathetic. 



Dr. Walker thinks that many of these "large" or 

 " exaggerated " variations running riot from time to time, if 

 left to themselves, would have come to ruin. But man came 

 to the rescue and protected (whilst exploiting) them. Again 

 we have thus the parallel with the case of algae and Convoluta. 

 In some cases when the exploitations of a plant by man has 

 finally transformed it into a monster, he ceases to cultivate it 

 and takes others under "cultivation" (exploitation), with the 

 same ultimate effects as in the case of the parasitic nurture of 

 algal cells by Convoluta. It all shows that eventual mutual 

 infertilitj'- is the result of retrogressive symbiosis, and, 

 inversely, eventual ability to blend the result of sufficient 

 symbiosis. 



The view that in domestication we are generally dealing 

 with an induced parasitic diathesis and a partial disruption 

 due to surfeit and the prevalence of anti-biotics, may also be 

 seen to receive corroboration from the following remarks of 

 Prof. Klebs in his contribution to Darwin and Modern 

 Science : 



It is, however, a fact that when a plant is removed from natural 

 conditions [from the bond of normal bio-economic co-operation] into 

 cultivation, a well-marked variation occurs. The well-known plant- 

 breeder, L. de Vilmorin, speaking of his own experience, states that a 

 plant is induced to "affoler," that is, to exhibit all possible variations 

 from which the breeder may make a further selection only after culti- 

 vation for several generations. The effect of cultivation was particularly 

 striking in Veronica chamcedrys which, in spite of its wide distribution 

 in nature, varies very little. 



After a few years of cultivation this "good" (sic) and constant 

 species becomes highly variable. The specimens on which the experiments 



