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SCIENCE 



[N. a Vol. XXV. No. 636 



producing the gametes is the gametophyte. 

 The stage arising from the germination of 

 the zygote is the sporophyte. All forms 

 which are hermaphroditic in the gameto- 

 phyte are of necessity hermaphroditic also 

 in the sporophyte. Every part of the 

 mucor species Sporodinia, therefore (with 

 perhaps exception of the sexual organs), 

 contains both sexes. The same is true of 

 some of the mosses and probably of all of 

 the homosporous ferns. No representatives 

 of this type exist among the flowering 

 plants. 



Phycomyces is diceuious in its gameto- 

 phyte. The zygospore formed by conjuga- 

 tion of branches from male and female 

 individuals produces at germination but a 

 single kind of germ tube which gives rise 

 to a sporangium containing both male and 

 female spores. The sporophyte therefore 

 is hermaphroditic. That the germ tube in 

 fact contains both male and female char- 

 acters may be proven by forcing it to grow 

 directly out to a vegetative mycelium before 

 the formation of spores. The growth thus 

 obtained is distinctly different from either 

 the male or female individuals character- 

 istic of this species and shows its possession 

 of both sexes by the fact that it produces 

 both male and female spores as well as 

 sexually formed zygospores. 



The liverwort Marchantia resembles the 

 mucors in that its gametophyte is multi- 

 plied by non-sexual reproductive bodies and 

 in that the sex of the spores of the sporo- 

 phyte is not apparent until after their ger- 

 mination. I have been able to show that 

 this liverwort corresponds to the Phy- 

 comyces type and its sporophyte must be 

 considered hermaphroditic since both male 

 and female spores are found in a single spo- 

 rangium. As with Phycomyces, the deter- 

 mination of sex does not take place in the 

 zygote but a sporophytic interval is inter- 

 polated between the zygote and the germ 

 sporangium where the segregation of sex 



finally occurs. The heterosporous ferns 

 illustrated by Selaginella differ from 

 Phycomyces and Marchantia chiefly in the 

 reduction in size of the gametophyte and 

 in the fact that male and female spores are 

 produced in separate sporangia. All four 

 types discussed are dioecious in gameto- 

 phyte while hermaphi-oditic in sporophyte. 



Mucor Mucedo has the sexes separated 

 on different individuals as in Phycomyces, 

 but two different kinds of germ tubes are 

 formed by the germination of its zygo- 

 spores. While some germ tubes are male 

 and produce only male spores, others are 

 female and produce only female spores in 

 the germ sporangium. The sporophyte as 

 well as the gametophyte therefore is uni- 

 sexual. The same is true of the dioecious 

 flowering plants represented by the poplar. 

 There are no ferns of this type and none 

 are known among the mosses, but the sexual 

 differentiation in the latter group has been 

 but little investigated. 



Forms like the bacteria apparently have 

 not developed sexuality, others seem to 

 have lost it. The loss may be permanent 

 as in the habitually parthenogenetic forms, 

 or merely temporary. Thus the sexual 

 races of one of the mucors has been ren- 

 dered temporarily neutral by cultivation 

 for a few non-sexual generations at un- 

 favorable temperatures and neutral races 

 of several species have been found in na- 

 ture. 



It is among the algje and fungi that the 

 influence of external factors upon the 

 method of reproduction has been most care- 

 fully investigated. The limits within 

 which growth is possible are further apart 

 than those within which the formation of 

 the reproductive bodies can take place. 

 Plants will grow under conditions where 

 they can not reproduce. Similarly the con- 

 ditions for the formation of sexual and 

 non-sexual reproductive bodies do not 

 always coincide, the limits being narrower 



