1919] 



Frost: Mutation in Matthiola 



127 



If we are dealing here with a type cytologically like Oenothera 

 gigas, or rather the triploid semigigas, abnormal distributions of 

 chromosomes may occur at meiosis, giving unpredictable genetic 

 results. There has been special difficulty, as the numbers of doubtful 

 individuals in table 26 suggest, in separating large-leaved from Snow- 

 flake, though in part of the cases the difference is extreme. Possibly 

 some of the doubtful individuals are genetic intermediates due to 

 irregular meiosis in triploid nuclei ; such irregularities in division 

 (Gates, 1915) occur with Oenothera. Both cytological examination 

 and crosses with Snowflake are plainly required. 



Table 28 



Crenate-leaved type: numbers of apparent mutants and association of the 

 type with singleness of flowers. 



° See note h to table 2. 

 " See note c to table 1. 



4. THE CEENATE-LEAVED TYPE 



This type (tables 1 and 3) is one of the three aberrant types of 

 most frequent occurrence in the cultures here described, having con- 

 stituted (table 28) about .79 per cent of the progeny of Snowflake 

 and early parents. A large majority of the individuals have been 

 singles, as table 28 shows. If the apparent mutants are produced by 

 some process of segregation of factors, evidently the crenate and single 

 factors were usually coupled in this material ; if they are produced 

 by immediate factor mutation, or are individually due to some change 

 in a particular locus, evidently that locus is linked with the single- 

 double locus and the change is more frequent in the single-carrying 

 chromosomes; and finally, if they are due to reduplication or loss of 

 a chromosome, the apparent linkage remains to be explained. 



The margins of Snowflake leaves vary from entire or slightly 

 sinuate to coarsely and irregularly dentate or serrate, this character- 

 istic being subject to much environmental modification and varying 



