704 



THE AMERICAN NATURALIST [Vol. XLIX 



regarded by Bartlett as a character new to the genus. Bartlett 

 emphasizes the fact that the characters of neither type could be 

 interpreted as the result of segregation following hybridization, 

 which may be true, but I do not think from this that it follows 

 that neither type can be the result of hybridization. I am not 

 willing to admit that hybrids present only combinations of char- 

 acters derived from their parent lines. It seems to me reasonable 

 to believe that in hybrids at times the interaction of elements 

 modifies the old or produces new factors. The species stenomeres 

 and the derivatives gigas and lasiopetala have not been tested for 

 genetic purity by cross-breeding with relatively stable types and 

 the problems of gametic and zygotic sterility have not yet been 

 attacked. 



The final paper of this group of Bartlett 's 3 deals with an ex- 

 tremely interesting situation developed in cultures of (Enothera 

 Beynoldsii from Knoxville, Tennessee. This is also a small- 

 flowered, close-pollinated species, and its peculiarity lies in an 

 ability to throw extraordinarily large classes of dwarfs. There 

 are two types of dwarfs: (1) semialta somewhat smaller than the 

 typical Beynoldsii and intermediate between it and the smaller 

 dwarf; (2) debilis. A plant of Beynoldsii in the F 3 produced 29 

 individuals like itself, 32 plants of semialta, and 18 of debilis, 

 i. e., 60 per cent, of its offspring were dwarfs. Semialta throws 

 debilis, but no Beynoldsii. Debilis apparently can produce no 

 Beynoldsii or semialta and breeds true except for an occasional 

 variant bilonga which was also found in one culture from typical 

 Beynoldsii. 



With respect to the dwarfs we have here presented a beautiful 

 series leading from the unstable parent type Hfynoldsii through 

 the more stable semialta to the most stable and most extreme 

 dwarf debilis. Bartlett calls the behavior mutation en masse, but 

 confesses that it bears a certain degree of resemblance to Men- 

 delian segregation. We should very much like to see this study 

 repeated on a larger scale and with experimental germination of 

 the seed so that we may be sure of the ratios and also certain that 

 the cultures have given us all of their possible progeny. Segre- 

 gation en masse seems to the writer likely to be a more probable 

 explanation of the phenomena than mutation. 



The form bilonga derived from the dwarf debilis offers a partic- 

 ularly interesting problem. It is similar to semialta except that 



» Bartlett, H. H., "Mutation en masse/' Amek. Nat., Vol. XLIX, 

 p. 129, 1915. 



