Apeil 3, 1914] 



SCIENCE 



485 



and left proximal tarsal segment, where 

 there is undoubtedly correlation, may be 

 open to objection under any consideration. 

 If, however, from the data presented in 

 the study the value of the coefficient of 

 variation is computed, which, strange to 

 say, was not done in the paper, and thus 

 allowance made for the greater length of 

 tibia in the cross-bred forms, the combined 

 inbred forms exhibit a variability rela- 

 tively 68 per cent, greater than the cross- 

 bred forms. 



Jennings (1911) in summarizing breed- 

 ing experiments with Paramecium con- 

 eluded that "The progeny of eonjugants 

 are more variable in size and in certain 

 other respects than the progeny of the 

 equivalent non-con jugants, " and farther, 

 "Thus conjugation increases variation." 

 Ck)ntinuing the investigations, he subse- 

 quently stated (1913) that conjugation in- 

 creased the variation in the rate of repro- 

 duction. While the careful methods used 

 by Jennings have brought to light many 

 interesting and valuable facts, it is evident, 

 from a critical consideration of the data, 

 that they by no means allow such conclu- 

 sions. 



So far as size is concerned in a pure 

 race, non-eonjugants and their progeny 

 were more variable than eonjugants and 

 their progeny, as noted in Table No. 28. 

 In a wild race the progeny of the eonju- 

 gants were slightly more variable than the 

 progeny of the non-conjugants, as illus- 

 trated in Table No. 32, although in two of 

 the nine generations tabulated the varia- 

 bility was greater in the case of the non- 

 conjugants. So far as the rate of fission 

 is concerned, the evidence is unmistakable 

 that the eonjugants were more variable. 

 There is, however, a comparatively simple 

 explanation for this when the statement 

 is noted that the number of abnormal in- 

 dividuals, as well as the mortality, was 

 greatest among the progeny of the eonju- 



gants. 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 be- 

 comes the more evident when it is found 

 that the higher variability of the eon- 

 jugants was caused by the considerable 

 number with the low rate of fission. 



Considering the data obtained in the 

 breeding of plant forms where the assump- 

 tion has long been prevalent that hybridi- 

 zation increases variability, it is found that 

 the variability of the Fj generation as com- 

 pared with the Fj generation or a single 

 parental generation may be increased, but 

 that the actual variability as a whole is not 

 increased when the united parental types 

 are taken into account. This may be illus- 

 trated by utilizing data from an interest- 

 ing paper by Hayes (1912) dealing with 

 correlation 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 decreased 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 dif- 

 ferent genotypes are bred together. Such 

 a condition may be illustrated by the two 

 white strains of sweet peas crossed by Bate- 

 son which produced purple flowers in the 

 first (PJ hybrid generation, and purple, 

 pink, mixed, and white flowers in the sec- 

 ond (F„) hybrid generation. New combi- 

 nations 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 of cross breeding or conjuga- 

 tion is of decided interest inasmuch as facts 

 bearing on the solution of the problem as 

 to how size may be increased to the phys- 



