FACTOR RELATIONS IN QUANTITATIVE INHERITANCE 179 



factor differences, differing, therefore, in no respect from those other 

 Mendelian differences concerning which no question is raised. 



The Cotton Leaf Factor. Leake has investigated the inheritance of 

 the so-called cotton leaf factor. The results of his investigations are 

 given here in some detail because they illustrate very well the simplest 

 expression of the most common type of quantitative inheritance. The 

 so-called cotton leaf factor is essentially a length breadth index of the 

 terminal lobe of the leaf. It is obtained by dividing the difference 



Parents 



Leaf-Factor 1.1 

 Values 



1.6 



3.6 



4.1 



2.1 2.6 3.1 



Type 4 x Type 8 



FIQ. 86. Distribution of parental, Fi, and Fz plants with respect to leaf-factor values. 



(After Leake.) 



between the two measurements a and b in the accompanying diagram 

 (Fig. 84) by the width c of the terminal lobe, or expressed algebraically 



it is the value of the expression Although there are variations 



C 



in this value for different leaves on a single plant, Leake found that races 

 might be obtained which were characterized by relatively constant leaf 

 factors. Leake crossed one of these races with a mean leaf factor of 

 1.52 with a race the mean leaf factor of which was 3.47. The mean leaf 



