70 Plant Genetics 



contained. His results, therefore, do not seem so clear 

 and striking as those of Nilsson-Ehle, but they are by 

 no means vague and uncertain. For example, even if he 

 could not say definitely that a certain individual had 

 exactly three doses, he could always say approximately 

 how many doses it had; and the breeding results always 

 confirmed the idea of a number 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 individuals on the basis of the 

 number of doses is more or less obscured by the influ- 

 ence of outside factors which are uncontrollable, or at 

 least uncontrolled as yet in breeding work. 



East has visualized these outside factors and dis- 

 cussed them. In order to explain this discussion, 

 . however, we must recall a feature of genetics which 

 has previously been mentioned. Plant variations in 

 the largest sense fall imder two categories, due to 

 (i) differences in gametic constitution, and (2) responses 

 to environment. The first category is the basis of all 

 Mendelian conceptions, while the second category in- 

 cludes such variations as are usually thought not to be 

 inherited, being acquired characters. This category 

 is now commonly called fluctuating variations. 



An illustration will make these two categories clear. 

 Assume that a plant with a determiner for tallness 

 usually 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 



