MUTATIONS 283 



tral characters. The controversy which arose over these questions 

 stimulated investigation to such an extent that the (Enothera literature 

 of the past decade would fill many volumes. These investigations have 

 proceeded along three definite lines: (1) crossbreeding experiments, 

 (2) cytological studies, (3) observations and collections in the field to- 

 gether with pedigree cultures. The last of these can only be mentioned. 

 See the recent reviews of Davis and Bartlett where further references 

 are given. The results of the other two bear directly upon the problem 

 of classifying de Vries' original "mutations." 



Concerning the first method of investigating the genetics of (Enothera, 

 there have been many crossbreeding experiments in both Europe and 

 America. Until recently most of the data derived therefrom have been 

 viewed as impossible of interpretation on a Mendelian basis. But since 

 1914 certain investigators have come to believe that breeding experi- 

 ments with (Enotheras have very little value as a means for exact 

 genetical analysis unless complete germination of all viable seeds is 

 assured. In that year Renner pointed out that seed sterility in the 

 evening primroses may cause apparent nonconformity with Mendelian 

 principles. Following up this suggestion with seed germination tests 

 and breeding experiments in which all viable seeds were germinated, 

 Davis came to the conclusion "that large proportions of (Enothera seeds 

 sprout in the earth only after many weeks or even months and that this 

 habit of delayed germination must have given in many of the cultures 

 described in the (Enothera literature hardly more than glimpses of the 

 genetical possibilities. We cannot feel certain that the records of any 

 cultures of (Enothera so far reported are complete for their possible 

 progeny, and consequently the ratios of classes described in breeding 

 experiments and the percentages of 'mutants' calculated cannot be ac- 

 cepted as final in exact genetical work. We are not in a position even 

 to guess what may be the change of front when exact data become avail- 

 able. . . . Consequently we have at present in the (Enotheras no 

 standard material of genetic purity with which forms under suspicion 

 may be confidently mated to determine by crossbreeding the uniformity 

 of their viable gametes. Until such material is discovered we shall be 

 working largely in the dark in our attempts to analyze the genotypic 

 constitution of (Enotheras." The same author, is inclined to interpret 

 data from his most recent (Enothera breeding experiment (biennis and 

 franciscana) as giving "positive evidence of a segregation of factors in the 

 F 2 generation of a character to be expected in Medelian inheritance." 

 This inference is the more noteworthy inasmuch as in the past this author 

 has not committed himself positively to a Mendelian interpretation of 

 any particular data on the (Enotheras. That certain characters in this 

 group are conditioned by specific genetic factors, seems to be generally 

 accepted. For example, it is highly probable that the deeply pigmented 



