THE ASSOCIATION OF CHARACTERS 297 



External influences can affect a plant only because of 

 some kind of responsiveness which must be present in it. 

 Without such no reaction will be produced. This assertion 

 may seem to be a truism, but even as such it m.ay help us 

 to reach a better view of the relation under discussion. 

 For it is clear that a parallel action of the external factors 

 demands a corresponding response of the cliaracters to them, 

 and we may base our discussion upon this assumption, 

 making the state of sensibility its chief aim. 



As a rule, all variable parts are influenced by the same 

 factors. Among them the nutritive are most prominent. 

 Other agents, such as temperature, moisture, and light, 

 cooperate with these in a more or less considerable degree. 

 Many authors, however, take their significance to be only 

 secondary, inasmuch as the nourishment itself may be 

 changed by them. On the basis of this conception, nutrition 

 would be the main factor in all fluctuating variabiHty. 



Now it is evident, that all development depends in the 

 first place upon the amount of available food. This simple 

 sentence gives a key to at least a large group of the phe- 

 nomena of correlation. Whenever the size of the seeds 

 increases with the weight of the whole harvest, or the number 

 of seeds in a pod with the height and degree of branching of 

 the plant, there can be no doubt that all these qualities 

 depend upon the nourishment, and that it is this factor 

 which causes them all to increase or to decrease at the same 

 lime. 



This rule will be more easily understood if we take a 

 definite example. As such I choose a variety of cultivated 

 poppies, belonging to the ordinary tall species or opium- 

 poppy (Papaver somniferum). Numerous forms of this 

 beautiful plant are cultivated in our gardens. The most 

 pecuhar among them is the variety in which the stamens 

 are partly converted into pistils. These secondary pistils 



