CURRENT LITERATURE 



NOTES FOR STUDENTS 



Oenothera genetics. — Heribert-Nilsson 1 discusses the data from his 

 studies of Oenothera Lamar ckiana, suggesting what he calls a Mendelian inter- 

 pretation of the mutating tendency of this species. The character with which 

 he worked was the red pigmentation found in the leaf nerves of some of his 

 plants and absent in others. He concludes, that the red-nerved and white- 

 nerved plants form a distinct discontinuous variation; that the white-nerved 

 plants are pure recessives and when selfed or intercrossed produce only white- 

 nerved plants; that a homozygous dominant is not formed, and that there- 

 fore a strain of pure red-nerved plants cannot be produced, but all red-nerved 

 plants when selfed or intercrossed will produce some white-nerved plants. 

 Finding the average ratio of red-nerved to white-nerved plants in O. Lamarck- 

 tana and most of its "mutants " to be 2 . 68 : 1, or nearly 3:1, instead of 2 : 1 as 

 would be expected when no positive homozygotes are formed, he adopts the 

 explanation proposed by Wilson in explaining the work of Cuenot with 

 yellow mice. According to this explanation, most of those positive female 

 gametes which would normally be fertilized by positive male gametes, but which 

 for some reason cannot be so fertilized, are fertilized by recessive male gametes. 

 This would produce an average ratio of the red-nerved to white-nerved plants 

 a little lower than would be the case under normal genetic behavior, thus 

 accounting for a ratio of 2.68:1 instead of 3:1. It should not be forgotten, 

 however, that the work of Castle removed the necessity for this interpre- 

 tation in the case of yellow mice, and thus lessened its value as an interpreta- 

 tion of this sort of deviation from expected ratios. 



In "gigantea" (the gigas type) the author interprets the observed ratios 



1 



as modifications of 3 : 1, 15 : 1, 63 : 1, and 255 : 1, and concludes that in this type 

 the red-nervedness is probably produced by any one of four factors. He also 

 finds that the factor or factors for red leaf nerves affects other morphological and 

 physiological characters of the plant. 



Having thus striven for a Mendelian interpretation of the behavior of 

 red vs. white nerves, the author presents his observations on the mutation 

 ratios of O. Lamarckiana and its mutants, or, as he calls them, " Kombinante," 

 and suggests the following explanation of the mutating tendency of this species. 

 O. Lamarckiana is dependent upon a number of groups of multiple factors, the 

 majority of which cannot be produced in a homozygous dominant condition, 



1 Heribert-Nilsson, N m Die Spaltungserscheinungen der Oenothera Lamarck- 

 iana. Lunds Univ. Arsskrift 12:4- 131. 1915. 



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