88 THE SHORTER SCIENTIFIC PAPERS 



illustrated in Table No. 32, although in two of the nine 

 generations tabulated the variability was greater in the 

 case of the non-conjugants. So far as the rate of fission 

 is concerned, the evidence is unmistakable that the con- 

 jugants were more variable. There is, however, a com- 

 paratively simple explanation for this when the statement 

 is noted that the number of abnormal individuals, as well 

 as the mortality, was greatest among the progeny of the 

 conjugants. With a considerable number of forms thus 

 having a lower rate of fission, one could expect nothing 

 except a greater variability in the rate of fission. This 

 becomes the more evident when it is found that the higher 

 variability of the conjugants was caused by the consider- 

 able number with the low rate of fission. 



Considering the data obtained in the breeding of plant 

 forms where the assumption has long been prevalent that 

 hybridization increases variability, it is found that the 

 variability of the F2 generation as compared with the Fi 

 generation or a single parental generation may be in- 

 creased, but that the actual variability as a whole is not 

 increased when the united parental types are taken into 

 account. This may be illustrated by utilizing data from 

 an interesting paper by Hayes (1912) dealing with corre- 

 lation and inheritance in tobacco. Here, calculating the 

 constants for two parental types combined (401 and 403) 

 in respect to number of leaves and height of plant, it is 

 found that the coefficient of variation has decidedly de- 

 creased through the hybridization, although the number 

 of combinations have increased. 



There exists the possibility, however, that variability 

 will appear to be increased when forms having the same 

 phenotype but different genotypes are bred together. 

 Such a condition may be illustrated by the two white 

 strains of sweet peas crossed by Bateson which produced 

 purple flowers in the first (Fi) hybrid generation, and 

 purple, pink, mixed, and white flowers in the second (F2) 

 hybrid generation. New combinations occur, but there 

 is no evidence of increase in unit characters, nor is there 

 an actual increase in variability. 



Turning for a moment to size characters, the influence 



