ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 307 



mosomes although phenotypically asexual. To this class can be 

 assigned at present with certainty only two species of Sphccrocarpos: 

 S. Donnellil, discussed in the present paper, and S. tcxanus, in 

 which Miss Schacke (1919) has recently found a condition as to 

 chromosomes similar to that in S. Donnellii. It may be hazarded, 

 however, that here belong also the dioecious mosses upon which the 

 epoch-making studies of the Marchals (1907, 1909, 191 1) were 

 made ; the heterozygous sporophytes of these mosses were induced 

 to give rise by regeneration to diploid and hermaphroditic game- 

 tophytes. 



The differences in the apparent relations of the chromosomes in 

 question in the organisms representing these three classes are 

 brought out strikingly by the facts that in class a two X-elements 

 are necessary to the appearance of femaleness, but only one X-ele- 

 ment (with or without a Y-element) to that of maleness ; that in 

 class b, two X-elements are requisite to the appearance of maleness, 

 and only one X-element (with or without a Y-element) to that of 

 femaleness ; whereas in class c the presence of one X-element means 

 femaleness, that of one Y-element maleness, and the presence of 

 both, under ordinary conditions, is correlated with non-sexuality. 



Another difference, at least as between the plants of class c on 

 the one hand and the animals of class a on the other, lies in the 

 apparent lack of function in h-eredity of the Y-chromosome or 

 -element in animals, as shown by its utter absence in many forms 

 and by the genetic evidence of its failure when present to influence 

 the transmission of sex-linked characters; although Bridges' (1916) 

 evidence in this connection should be cited, namely, that the absence 

 of the Y-chromosome in Drosophila, while not affecting the appar- 

 ently normal development of the male animal, does result in steril- 

 ity. In Sphccrocarpos, however, there is no reason at present for 

 considering the Y-chromosome to be in any sense a functionless 

 body. Its presence seems, as will be indicated more fully in a later 

 paragraph, to be related to the appearance of definite characters in 

 just as positive a way as is the presence of the X-chromosome. 

 And in the normally dioecious mosses studied by the Marchals, 

 heterozygosis in the diploid gametophyte manifested itself by the 

 appearance of both male and female characters. 



