Proceedings of the Ohio State Academy of Science 337 



sexual, the male gametophytes are the smaller while the larger 

 females are also more branched. There is thus a normal sexual 

 dimorphism of the vegetative body. The thalli are influenced 

 to a certain extent by external conditions and unfavorable con- 

 ditions of nutrition tend to increase the proportion of males. 

 But what is still more important, it has b( ?n demonstrated that 

 Equisetum thalli which have developed ovaries, namely devel- 

 oped as females, can l)y insufficient nutrition be forced to pro- 

 duce spermaries. It is evident, therefore, that the thalli have 

 not developed unisexually, as male or female, through some in- 

 herent difference in their constitution nor through the loss of 

 male or female sex determining characters, but rather that one 

 set of tendencies has become latent while the opposite set is 

 active. The latency is however not permanent but can be over- 

 come by a proper environment. 



E'. and E'. Marchal have shown that in certain mosses, 

 Barbula unguiculata. Bryum argentium, and Ceratodon pur- 

 pureus, the gametophytes are strictly male and female and are 

 produced in equal numbers from the spores of one sporangium. 

 Now these mosses may regenerate secondary protonemata from 

 fragments of the gametophyte, stem, scale or rhizoid, and in 

 every case the sex character is faithfully continued. The sex 

 could not be changed by varying the conditions of environment. 

 By regenerating parts of the sporophyte which has the diploid 

 number of chromosomes the ]\Iarchals obtained protonemata 

 which are hermaphrodite rather than unisexual as those pro- 

 duced from the spores or gametophytes. The great majority, 

 however, showed only male characters and a few developed 

 only female characters. But the one sex was only latent as was 

 shown by the possibility of obtaining hermaphrodite individ- 

 uals again from these diploid, unisexual forms. 



Now it is evident that two interpretations may be made of 

 these phenomena. First, the spore gametophytes which were 

 apparently unisexual contained the characters of both sexes, 

 one set being latent ; second, the hereditary characters of one 

 sex only were present. The ]\larchals adhere to the second 

 hypothesis. Were this the condition of things generally, one 



