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THE AMEBIC AN NATURALIST [Vol. XL VIII 



strain is decreasing in the average annual shift of the 

 mean. 



Family No. 41 shown in Table X gave perhaps the most 

 peculiar results of any of the selections. It may be that 

 no great shifting of the mean toward the minus end of the 

 curve should have been expected, because the minus 

 mothers were each rather high in number of leaves. There 

 was one with 25 leaves and one with 24 leaves. This was 

 unfortunate, but was made necessary by the number of 

 late and diseased (mosaic) plants in the selection. Never- 

 theless, each of these plants was below the mean of the 

 previous generation and if a marked change would have 

 followed the selection of extreme individuals, some change 

 should have followed the selections of the individuals that 

 were the actual mothers. But in spite of this fact the 

 mean persistently rose from 23.9 ± .07 leaves to 26.3 ± .08 

 leaves, then to 28.1 ± .07 leaves, although the duplicate of 

 this selection grown in 1912 went down slightly to 27.4 

 ± .07 leaves. In the plus strain successive generations 

 of mothers having 28 and 30 leaves caused a small upward 

 shift of the mean ; it became first 25.7 ± .09 leaves then 

 25.6 ± .14 leaves, although the 1912 duplicate of the last 

 population had a mean of 26.9 ± .08 leaves. 



The extraordinary phenomenon to which we wish to 

 call particular attention, however, is not this behavior of 

 the minus and plus strains in the regular selection ex- 

 periment, but rather the origin of a few-leaved strain 

 from a single individual that appeared in the F 6 genera- 

 tion of the plus strain. Eef erring to the table, it will be 

 seen that in this generation a 12-leaved plant appeared. 

 This is really a peculiar phenomenon, for we had never 

 before observed a normal 12-leaved plant among the many 

 thousands that have come under our observation. They 

 do not occur. In this population the plant with the next 

 lowest numbers of leaves had 20 leaves, and in classes 20 

 and 21 there was only a single plant of each. This 12- 

 leaved plant was selfed and gave rise to a population 

 ranging from 8 leaves to 30 leaves, and having a vari- 

 ability of 23.50 per cent. ± .11 per cent. The mean of the 



