MUTATIONS 285 



less characters have been discovered that appear to be inherited according 

 to simple Mendelian rules. We conclude, therefore, that some of the 

 lamarckiana derivatives are the result of factor mutations. 



The cytological studies on (Enothera have yielded important infor- 

 mation concerning the chromosome numbers of various species and "mu- 

 tants." With reference to (E. lamarckiana and its derivatives especially 

 the chromosome counts of Miss Lutz, Gates, Davis and others are of 

 great interest. Lamarckiana has 14 chromosomes as have also most of 

 the "mutants" which have been derived from it, but the sexually 

 deficient and inconstant form, lata (see Fig. 116) has been found always 

 to have 15 chromosomes. Furthermore, actual cases of a distribution 

 of 6 + 8 chromosomes in the heterotypic division of pollen mother cells 

 have been observed in lamarckiana and rubrinervis. It is safe to assume, 

 therefore, that lata-like "mutants" result from the union of a gamete 

 containing 8 chromosomes and one containing the normal number, 7. 

 There is also good evidence that (E. gigas is the result of tetraploidy. 

 Several different plants of this type have been found to contain 28 chromo- 

 somes or thereabouts. However, there is a giant race of the Chinese 

 primrose which has only 24 chromosomes, the number typical of the 

 species, while another has 48 chromosomes. It seems then that gigan- 

 tism is associated with tetraploidy but that it is not necessarily caused 

 by an aberration in chromosome number. Thus we find that at least 

 one, and perhaps another of the original lamarckiana derivatives are 

 due to chromosome aberrations during meiosis. 



Of the nine original mutants we have now definitely classified two 

 brevistylis as a factor mutation and lata, the result of a departure from 

 normal chromosome number, and we have found that a third, gigas, 

 exhibits an extreme chromosome aberration. What about the remain- 

 ing six Icevifolia, albida, oblonga, rubrinervis, nanella and scintillansf 

 There is no evidence of a simple factorial relation between them and the 

 parent species. One of them, scintillans, must remain in the doubtful 

 class until its chromosome numbers have been determined, but the 

 inconstancy of this form suggests that it should be classed with lata 

 and gigas under chromosome aberrations. The remaining five, Icevifolia, 

 rubrinervis, nanella, oblonga and albida, are known to have 14 chromo- 

 somes. Based on the evidence set forth in Chapter XII, it seems to 

 us that one and only one category is open to these five forms and that 

 probably albida, oblonga and most of the new forms that have appeared 

 not only in cultures of lamarckiana and its derivatives but also in other 

 species of (Enothera, are the result of chance recombinations of factors 

 due to a condition of substrate hybridity. This expression, as has already 

 been explained, is meant to imply that "mutating" species such as OS, 

 lamarckiana are merely species hybrids which happen to result from 

 combinations of different reaction systems such that the majority of 



