Methods of Investigation. 523 



what part 6i the result of selection is due to this accumu- 

 lation of nutrition during the succeeding generations? 



These considerations tend to draw selection and nutri- 

 tion closer and closer together. The exact morle of 

 nutrition seems to me a matter of secondary importance; 

 what is of the first importance is to discover tlie effects 

 of nutrition on the susceptible periods in development, 

 and to study the accumulation of this effect in the course 

 of some generations. Now, just as nutrition reaches its 

 maximum effect, in practice, in the course of a few gen- 

 erations, so the limit reachable by selection is very soon 

 attained.^ The significance of the parallel between these 

 two limits seems to me to be obvious. 



The closer variability is drawn towards nutrition the 

 wider becomes the gulf between variability and muta- 

 bility. 



§ 2. METHODS OF INVESTIGATION. 



The effect of nutrition and selection can either be 

 exerted in similar or in opposite directions; the sum of, 

 or the difference between, their effects can thus be de- 

 termined. 



The general effect of both factors is well known. We 

 are not concerned to prove that the, effect of high nutri- 

 tion is to produce large fruits, and that that of insuffi- 

 cient manure is to produce small ones, and so forth. It 

 seems more important to show that the number of ray- 

 florets can either be increased or diminished by selection : 

 but even on this point there is no doubt whatever. 11ic 

 only question is which of these two factors will pre- 

 ponderate in given instances? 



' Part I, § 9, p. 85. 



