FISSION RATE OF STYLONYCHIA PUSTULATA 491 



being for the three successive ten-day periods respectively 1,99 

 per cent, 4.36 per cent, and 7.10 per cent of the total number of 

 generations produced in the given period. 



The gradual increase of the difference between the two sets 

 indicates that this difference was heritable. This gradual in- 

 crease is well shown in the curves of figure 14, giving at a, the 

 average number of generations produced per three-day period 

 by each set, at h the curve of the differences in favor of the fast 

 set. Figure 15 gives the curves of variation of the total number 

 of generations produced by the two sets, showing that they 

 overlap very little. The evidence indicates strongly that the 

 effect of selection is cumulative. 



Experiment 3-B. To test whether the difference produced by 

 selection is actually heritable, balanced selection was now prac- 

 ticed for twenty-one days, October 21 to November 10, 1914. 

 On every day but one (the second) the lines that had been sub- 

 jected to fast-selection averaged higher than others. Table 14 

 gives the actual numbers of generations per line for the two 

 ten-day periods. 



Table 14 shows that during both of its periods the fast lines 

 averaged more generations than the slow ones and further that 

 the per cent that this difference is of the total number of gener- 

 ations produced by both together was practically constant. 

 Figures 14-c and 14-d show the average difference of fission rate 

 between these two sets of lines, averaged for three-day periods. 

 These two figures emphasize the marked uniformity of this 

 average difference. Hence this experiment shows that the oppo- 

 site selection previously practised had produced a nearly uni- 

 form heritable difference of average fission rate between the two 

 halves of this second clone. The results are thus the same as 

 in our first set of experiments. 



Experiment 3-C. Effects of conjugation on the results of 

 selection. 



It appeared of interest to determine whether these inherited 

 results of selection would persist through conjugation. It is well 

 known that conjugation is an ordeal having many effects on 



