8o 



Outliiie of Genetics 



behave exactly alike; the same is true of 6-foot plants. 

 It must be evident, therefore, that a classification of 

 F2 individuals on the basis of the number of doses might 

 well be slightly obscured. If outside influences were 

 lacking, the F2 situation could be represented by fig. 13 ; 



Fig. 13. — Diagram illustrating distribution of phenotype classes in 

 Yi population from cross involving cumulative factors. Practically 

 same diagram as fig. 12, and interpreted in same way; short rectangle 

 at left indicates that very few plants of population contain maximum 

 number of doses; short rectangle at right indicates that very few plants 

 contain minimum number of doses; plants with intermediate number of 

 doses most numerous, as indicated by tall rectangle in middle (see also 

 fig- 14). 



but when outside influences are active, it may be repre- 

 sented by fig. 14. It will be seen from this last diagram 

 that not all individuals belonging to a particular size 

 class may have the same number of doses; that is, con- 

 ditions surrounding the development of a smaller-dosed 

 individual may be so much better than those for a larger- 

 dosed individual that they may exchange size classes in 

 the result. In this way, the results of germinal constitu- 



