522 Influence of Nutrition and SetectioH. 



seed on the motherplant has, in many cases at any rate,^ 

 a greater effect on variabihty than nutrition during ger- 

 mination and vegetative Hfe itself. 



It seems to me that these principles which I only 

 appreciated after many years of experimenting, are now 

 perfectly clear and evident. 



From these principles there follows the experimenta' 

 method which I call the Principle of the manuring of ihc 

 parent-plant. That is to say, the effect of manuring 

 on variability must be studied not only on the plants 

 which have been heavily manured, but mainly on the 

 generation produced by their seeds. 



These principles lead to a further problem, the solu- 

 tion of which will perhaps be of great importance from 

 the point of view of the theory of selection. For it is 

 clear that the principle of the manuring of the parent- 

 plants is not necessarily confined to one generation. We 

 shall obviously not get the best nourished seeds from ill 

 favored parents; that is from parents which have them- 

 selves arisen from poor seeds. On the contrary the 

 operation of high nutrition of the seeds must be capable 

 of accumulation through two or more generations. The 

 same is true of low or defective nutrition. But inasmuch 

 (as a general rule) those individuals which exhibit the 

 character dealt with in a high degree are the best nour- 

 ished we naturally choose the most highly nourished 

 individuals as seed-parents when we are selecting for any 

 particular character. In the course of generations the 

 effect of nutrition accumulates, and in this way the devia- 

 tion of the particular character from the original type is 

 continuously increased. The question arises therefore : 



^ Sometimes, however, a greater effect can be produced on varia- 

 tion by a good or bad treatment of the seedhngs than by the choice 

 of seeds ; for example in Papaver somniferum polycephalum. 



