118 University of California PitbJicationit in Apriciiltural Sciences [Vol.4 



This corresponds well enough with the monohybrid expectation of 

 5 : 10 : 5 ; in fact, the deviation is just such as would be expected if there 

 was occasional cross pollination of the unprotected flowers of WG9- 

 ClO from Snowflake plants. The large proportion of evidently pure 

 late parents is strong evidence for the monohybrid nature of WG9-C10. 



The proportions of the two types among the doubles can only be 

 estimated. The 1908 data suggest that 5 of the 10 doubles there 

 reported were early ; this number, with the 13 singles so classed, makes 

 a total of 18 early-type plants out of 30. The ratio is slightly nearer 

 to 1 : 1 than to 3 : 1, and the former proportion would suggest the 

 peculiar type of inheritance found with the mutant types yet to be 

 described. The evidence of the 1910 distributions, however, shows that 

 the early type largely predominates in the next generation with both 

 singles and doubles, and apparently this is true even when we exclude 

 the progeny of the one parent classed as pure early. 



The early factor can be positively detected only by progeny tests. 

 No test has shown the presence of this factor elsewhere than in WG9- 

 ClO and part of its descendants. WG9-C10 produced the earl,y and 

 Snowflake types among 20 single progeny nearly in the typical mono- 

 hybrid proportions. Inspection of the double progeny in two genera- 

 tions suggests similar or possibly somewhat lower proportions there. 

 A vicinistic origin for WG9-C10 is improbable. Presumably, then, 

 the early type arose from Snowflake by a single factor mutation, the 

 dominant mutant factor being inherited without special complications. 

 We shall now consider certain apparently mutant types which are 

 characterized by peculiar genetic behavior. 



2. THE SMOOTH-LEAVED TYPE 



This type was first observed in the cultures of 1908 (table 1) and 

 ha.s occurred frequently in later cultures (table 3). It is perhaps the 

 mutant type of most frequent occurrence among progeny of Snow- 

 flake or early parents; 2410 unselected progeny from house-sown seed 

 of such parents (see table 28) included 28 apparent mutants (14 

 singles. 11 doubles, and 3 undetermined), a mutation coefficient of 

 1.16 ± .15 per cent. 



As grown in the greenhouse at Ithaca, this type (fig. 7, tables 12 

 and 13) was often many-noded, with correspondingly late flowering. 

 Its most striking peculiarity, shown especially by young seedlings and 

 not evident in the figures, was a lack of buckling between the veins 



