No. 565] CHANGES PRODUCED BY SELECTION 



27 



field is not clear. It is possible that the plants having 

 from 18 to 23 leaves were diseased, but no such condition 

 could be recognized in the field. Again, it is possible 

 that a few Havana plants were mixed in by mistake, 

 although as the leaves of the selection are characteris- 

 tically different from Havana and as the plants with low 

 leaf numbers resembled the remainder of the row, this 

 supposition is improbable. The most likely explanation 

 is that mutation occurred in a few gametes of the mother 

 plant, a condition that did arise, or that we assume to 

 have arisen, in Family 41 (see Table X). At any rate, 

 the change did not folloiv the path of selection. 



In Figs. 6 and 7 are shown typical plants of Family No. 

 6 obtained by three years of selection in the effort to pro- 

 duce strains of high and low leaf number, respectively. 



Family No. 34 (Table VIII) is peculiar— although this 

 is not the only time the phenomenon occurred — in that 

 the F 5 population grown from a 24-leaved F 4 plant seems 

 not to have given the true mean. Plants with a low num- 

 ber of leaves (22 and 20) were selfed to carry on the 

 minus strain, but both gave means higher than was shown 

 by the F 5 generation. Perhaps further selection will 

 produce results, but the case is not a hopeful one. The 

 only evidence for such an assumption is the increased 

 mean of the F 7 plus strain. If it is assumed that 24.0 is ' 

 nearer the true mean of the F 5 population than the 22.9 

 actually calculated, then the jump to 27.0 ± .08 leaves in 

 the F 7 generation gives us a basis for expecting results in 

 F 8 in the minus strain. 



Nothing can be said as yet about the minus strain of 

 Family No. 12 (Table IX),* for it happened that the first 

 selection was a complete failure. Six plants were ob- 

 tained, but the lowest number of leaves was 29. One of 

 these plants was selfed and gave an F 7 population having 

 a mean of 28.7 ± .09 leaves. Unfortunately the selections 

 from this fraternity did not germinate and in 1912 we had 

 to fall back on the reserve seed from which the 1911 crop 

 came. The crops of 1911 and 1912 are therefore dupli- 

 cates. The plus strain made an advance from 24.5 ± .10 



