16 



THE AMERICAN NATURALIST [Vol. XLVIII 



the F 2 generation of the reciprocal cross where the mode 

 was at 24 to 25 leaves. The F 6 fraternity that it pro- 

 duced was somewhat smaller than one would wish if 

 he were to, be confident of the calculations made. The 

 mode is 22 leaves and the mean nearly the same, 22.4 

 ± .11 leaves. From among these plants, a minus variant 

 having 20 leaves and a plus variant having 27 leaves were 

 selected to produce the F~ generation. The modes in this 

 generation are 21 and 25 leaves, respectively, a difference 

 of 4 leaves; and the means are 21.9 ± .08 and 24.9 ± .11 

 leaves, respectively, a difference of 3 leaves. Progress in 

 both directions continued when a 20-leaved plant was 

 selected to carry on the minus strain, and a 30-leaved 

 plant was selected to carry on the plus strain. The modal 

 classes of the F 8 generation are 21 leaves in the minus 

 selection and 26 leaves in the plus selection, while the 

 means are 21.3 ± .05 leaves and 26.6 ± .07 leaves, respect- 

 ively. In the F 9 generation the plus selection was lost, 

 but the minus selection grown from a 20-leaved plant had 

 the mode dropped to 18 leaves and the mean to 18.4 ± .08 

 leaves. In order not to lose the plus selection entirely, 

 however, more of the F 8 generation seed was grown in 

 1912. The mode is the same as in 1911, but the mean 

 dropped slightly to 25.8 ± .08 leaves. 



Here one notices what is very common throughout the 

 experiment ; the extremes selected for mother plants were 

 not members of the most extreme classes. This means 

 simply that vigorous healthy specimens were always 

 selected as the mother plants, and often the most extreme 

 variants did not come up to the standard. It is hardly 

 just to criticize this procedure, however, for with the best 

 care that it was possible to give, the experiments with 

 several families were terminated on account of non- 

 germination of seed or for some similar reason, it being 

 impossible, on account of the pressure of other work, to 

 self many plants in each selection. Even where seed 

 from several mother plants was collected, it did not in- 

 sure the continuation of that selection. The necessary 

 space and care involved in growing so many seedlings in 



