180 GENETICS IN RELATION TO AGRICULTURE 
factor of 28 Ff, plants obtained from this cross was 2.39, a value 
which does not differ significantly from the average leaf factor of the 
two parents, 2.49. Fig. 85 illustrates three leaves representing the three 
types concerned in this cross. From the F, plants of this cross 195 Fy», 
plants were grown, and their leaf factors were found to be distributed as 
shown in Fig. 86. The striking feature of this F, distribution is that, 
although practically all values for the leaf factor between the two parental 
extremes are represented, these frequencies of values give a trimodal distri- 
bution with modes which correspond approximately to those of the parents 
and the Fy. If these F, individuals be divided into three portions, as 
shown in Table XXXII corresponding to the two parents and the Fi, the 
mean value for the upper group is 3.42 as compared with the mean value 
of 3.47 for the corresponding parental type, the mean value of the mid 
group is 2.59 corresponding to 2.39 for the Fi, and the lower group has a 
mean value of 1.66 as compared with 1.52 for its corresponding parental 
group. In the upper group there were 46 plants, in the mid group 102, 
and in the lower group 47, a satisfactory agreement with a 1:2:1 ratio. 
TABLE XX XIJ.—RE&E-APPEARANCE OF PARENTAL VALUES IN THE F. OFFSPRING 
(After Leake). 
aa AA 
P Parent type No. 4 Parent type No. 8 
1 
Leaf factor 1.52 Mean 2.49 3.47 
F, | 28 plants Aa 
Mean leaf factor 
| 2.39 
| Classes Lower Middle Upper 
Leaf factor Less than 2 Greater than 2 Greater than 3 
Pr. Less than 3 
No. of individuals 47 102 46 
Ratio laa 2.2aA 1 AA 
Mean leaf factor 1.66 2.59 3.42 
This case then gives a simple expression of the general phenomena 
assumed to be operative in the multiple factor theory of size inheritance. 
If it be assumed that a single factor difference be here operative, then the 
small parent might be represented as aa and the large parent as AA. 
Plants of the genetic constitution aa then fluctuate for their leaf factor 
around 1.52 as a mean, whereas plants of the genetic constitution AA 
fluctuate around 3.47. When these two races are crossed the F; is 
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