INHERITANCE OF SEX IN MERCURIALIS ANNUA 
427 
worts has no relation to the reduction division, as appears to be the case in 
Sphaerocarpos. The spore that produces the gametophyte in such a form 
has the potentiahty of producing both sexes, both antheridia and archegonia 
being found on the same thallus. 
That ordinarily dioecious liverworts exhibit mixed sexuality in the game- 
tophyte has been observed in a few isolated cases. Taylor (1837) describes 
an androgynous gametophore in Dumortiera irrigua, Townsend (1899) 
found in Preissia commutata the male thallus bearing archegonia. Ernst 
(1907) found androgynous receptacles in Dumortiera velutina. Cutting 
(191 o) found that an archegoniophore of Marchantia polymorpha bore 
antheridia. Limpricht (1890) observed transitional structures between 
antheridia and archegonia in Jungermannia Kaurini and Cephalozia Gott- 
schei. Although the cases studied are few, fixity of sex or fixity of sex 
organs is apparently not absolute in the liverworts. The literature is, 
however, very meager upon this subject. 
Sex determination in the dioecious mosses may also occur at the reduc- 
tion division, that is at the division which forms tetrads. In the monoecious 
mosses no segregation of sex determiners at the reduction division can be 
conceived. There are a few cases among the dioecious mosses in which 
mixed sexuality occurs. Miiller (1848) found in Leucohryum giganteum 
the archegonia transformed into branchlets and no paraphyses present, 
while the perichaetium was excessively developed. Antheridia occurred 
on these female plants. The species is described as dioecious. Ruthe 
(1874) found that Physcomitrium eury stoma has three kinds of shoots, male, 
female, and hermaphroditic. He also found antheridia at the base of the 
archegonia in female shoots. Philibert (1883) found in Homalothecium 
fallax, Campothecium lutescens, and Fissidens bryoides that protonemata de- 
rived from dying leaves and parts of female plants produced small male 
plants. These mosses are described as being dioecious. Bergevin (1902) 
found mixed sex organs in Plagiothecium sylvaticum. He shows figures of 
archegonia transformed into antheridia, all stages in the transition being 
observed. His figures show a condition in which the archegonium can be 
recognized in part of the mixed structure, the other part being transformed 
into an antheridium. Wilson (191 5) found in Mnium hornum normal 
antheridia, bisexual organs, and modified archegonia on the same axis. 
The number of chromosomes was haploid, and it was not a case similar to 
that described by the Marchals (1907). 
In the prothallia of the homosporous ferns the succession in the appear- 
ance of antheridia and archegonia is modifiable by very many external 
conditions. According to Wuist (191 3), the gametophyte of Onoclea 
struthiopteris is normally dioecious. A monoecious condition can be in- 
duced by transferring the prothallia from one culture to another. If this 
be true, sex in such forms is determined at the reduction division but modi- 
fiable afterwards. 
