52 Mutations and Evolution. 



Cruciateness affords the most conspicuous and instructive 

 examples of parallel mutations among wild CEnotheras. There are 

 indications that the red hypanthium, which is the most conspicuous 

 feature of the mutant rubricalyx, may also be paralleled, though in 

 a less degree, by certain wild species. Thus CE. rubescens Bartlett 

 (1914b) has buds and hypanthia which are pale red. It would 

 appear to agree in this feature with the form, probably hybrid in 

 origin, which the writer 1 described from Lancashire under the name 

 CE. rubrincrvoides. A small-flowered undescribed species, CE. 

 cohtmbiana, from near Washington, is said by Bartlett to have 

 " conspicuously red hypanthia." The writer has pointed out else- 

 where* that the deep red of rubricalyx may become pale red by 

 crossing and then back-crossing with a greenish-budded species. 

 Thus in (CE. rubricalyx x grandiflora) x grandiflora, if the female 

 parent is heterozygous for the red factor, segregation into types with 

 red or green hypanthia will take place, but the red will be much paler 

 than in the selfed offspring of the female parent plant. In other 

 words, the colour is diluted and the red remains permanently pale 

 in the selfed offspring of such plants, deep red only being restored 

 by a back-cross with rubricalyx. Red or reddish hypanthia in 

 plants from all these different sources, indicate its appearance 

 through independent variations in different species. 

 Parallel Mutations in Drosophila. 



Various features of the Drosophila work have already been 

 discussed. In D. melanogaster (ampelophila) certain mutations have 

 occurred repeatedly. Thus (Morgan, 1919) white eyes have appeared 

 independently three times, vermilion eyes at least six times, rudi- 

 mentary wings five times, cut wing four times, truncate and notch 

 wings each several times, but in the last two cases the change 

 involved may not always have been the same. 



In the last five years a number of mutations in six other species 

 of Drosophila have been recorded. This includes a new eye-colour 

 (scarlet) in D. repleta (Hyde, 1915a), another sex-linked mutation 

 (light grey thorax) in the same species (Sturtevant, 1915), a wing 

 mutation (jaunty C) in D.confusa (Hyde, 1915b), one in D. tripunctata 

 (Metz and Metz, 1915), three mutations (extra bristles, triangle wing 

 veins and short wing veins) in D. obscura Fall., and one 

 (chocolate eye-colour) in D. similis Will, from Cuba (Metz, 1916b). 

 In " species B," now known as D. virilis Stt.,a more detailed study 

 1 Gates, 1914b. Gates, 1914a, 19J5f. 



