Feb., 1906.] Sexual and Nonsexual Generations. 473 



SEXUAL AND NONSEXUAL GENERATIONS. 



John H. Schaffner. 



Recently a number of ideas have been put forward bv 

 various authors as to what is a sexual or nonsexual individual 

 or generation. To the writer the case seems to be a matter of 

 definition. The confusion appears to arise not so much in a 

 misapprehension of the facts involved as in the extension of the 

 meaning of the terms used. But in this case individuals and gen- 

 erations should be judged by what they produce. 



A sexual generation is a gamete-producing generation. Any 

 individual, therefore, producing cells which normally are to 

 conjugate possesses sexuality provided the conjugation results 

 in reproduction. If there is a differentiation of sex, the indi- 

 vidual which produces female gametes directly is a female indi- 

 vidual, and the individual which produces male gametes directly 

 is a male individual. The gametes or male and female cells may 

 be produced with or without a preceding reduction division, for 

 the sexual generation may be either an " .v" or a " 2.v " generation. 



A nonsexual generation is a spore-producing generation, the 

 spores being non-conjugating reproductive cells. The non- 

 sexual generation may also be either an ".v" or a "2x" genera- 

 tion. Sex terms are, of course, not to be applied to nonsexual 

 generations or individuals. 



An alteration of generations may be antithetic having an 

 ".r" gametophyte and a "2a'" sporophyte. And certainh' the 

 generation which produces the sexual cells is to be called the 

 sexual generation and the one producing the nonsexual spores 

 the nonsexual generation. So in the higher as well as in the 

 lower plants the gametophyte is the sexual generation and the 

 sporophyte the nonsexual. An alternation of generations need 

 not be antithetic. But both generations mav have the ".v" 

 number of chromosomes. In such forms as Oedogonium and 

 Coleochaete, for intsance, where the 2.r number of chromosomes 

 appears to be only in the zygote, the organism coming through 

 reduction from the zygote is still the sporophyte and nonsexual 

 generation for the reason that it finally produces nonsexual 

 spores. It is possible that there are "2.v," sporophyte genera- 

 tions producing their spores without reduction which would 

 then occur before the formation of the gametes and we would 

 then have an alternation of generations with a "2.v-" gameto- 

 phyte and a "2a;" sporophyte. Here again the gametoph3"te is 

 the sexual and the sporophyte the nonsexual generation. In 

 other words, sexual and nonsexual individuals or gametophytes 

 and sporophytes are not determined by an ;v number or a 2.r 

 number of chromosomes but by the fact that the first produce 

 gametes and the second nonsexual spores. 



