Inheritance of Quantitative Characters 79 



tain. For example, even if they could not say definitely 

 that a certain individual had three doses, they could 

 always say approximately how many doses it had; and 

 the breeding results always confirmed the idea of a num- 

 ber of cumulative factors at work. For example, a 

 plant with three doses may vary with respect to the 

 character in question. It may approach the condition 

 of the plant with four doses or it may vary toward the 

 two-dose condition. Such variation may be explained 

 by outside influences. Any classification of the F2 indi- 

 viduals on the basis of the number of doses is more or 

 less obscured by the influence of outside factors which 

 are uncontrollable, or at least uncontrollable as yet in 

 breeding work. 



Emerson and East have visualized these outside 

 factors and discussed them. In order to explain this 

 discussion, however, we must recall a feature of genetics 

 which has previously been mentioned. Plant varia- 

 tions in the largest sense fall under two categories, those 

 due to (i) differences in gametic constitution, and (2) 

 those due to responses to environment. The first cate- 

 gory is the basis of all iMendelian conceptions, while the 

 second category includes such variations as are usually 

 thought not to be inherited, being acquired characters. 

 This category is now commonly called fluctuating varia- 

 tions. 



An illustration will make these two categories clear. 

 Assume that a plant with a determiner for tallness usu- 

 ally becomes 6 feet, while one without this determiner 

 becomes 3 feet. The 6-foot plant, however, grown in 

 good soil becomes 6.5 feet, while in poor soil it is 5.5 feet. 

 In inheritance, of course, the 6.5- and 5.5-foot plants 



