46 Experimental Zoology 



.when the environment that has caused them is altered. De 

 Vries answers this question in the following way : If the seeds 

 of the best-nourished ordinary plants are selected and planted 

 under the most favorable conditions, the average plants of the 

 next generation will not only be as vigorous as the former, but 

 their seeds themselves will have a higher average of size. If 

 this process is continued, the average of the race will be in- 

 creased in the direction of selection, and in time the race, i.e. 

 all the individuals, may be brought to and maintained near the 

 highest plane to which fluctuating variation ever reaches. 



There is a counteracting principle that must also be con- 

 sidered, viz., what Galton has called regression toward medi- 

 ocrity. If variations that depart from the average of the type 

 are united, their descendant will tend in some degree to return 

 to the average or to mediocrity, as Galton has shown. If, 

 however, we pick out in each generation those that are most 

 above the average, the average of the descendants in each gen- 

 eration rises, despite the regression, and in time the average may 

 be brought near to the highest point to which individual varia- 

 tions reach. In other words, the character that appeared in 

 the first generation as a somatic variation of one individual 

 has become temporarily transferred to the seeds; but unless the 

 same favoring external conditions are vigorously maintained, 

 there will be a return to mediocrity. 



This fastening, as it were, of the individual variation upon 

 the race is due, de Vries thinks, to the action of the nourish- 

 ment on the germ-cells. 



If a plant is well nourished, it produces larger seeds that are 

 better supplied with nourishment. Hence on an average they 

 will give rise to more vigorous plants, and these in turn will 

 produce an average of larger or at least of better-nourished 

 seeds, and the plants from these will be still stronger. Thus 

 by slow degrees the seeds acquire the same sort of characteris- 

 tics as those shown by the best-nourished plants in any one 

 generation. The curious thing about this is that the seeds do 

 not respond completely in the first generation, but it takes sev- 



