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 
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Values Type 4* Type 8 
Fra. 86.—Distribution of parental, 71, and F, plants with respect to leaf-factor values. 
(After Leake.) 
between the two measurements a and 6 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 
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 
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