438 Wilson,—Sex Determination in Mnium hornum. 
no conclusion could be arrived at on account of the failure of germination of 
some of the spores; in four groups the results did not agree with the 
supposition that two male and two female spores were present in the tetrad. 
Strasburger accepts this as proof that sex separation takes place at the 
division of the spore mother-cells, and results in the formation of two male 
and two female spores. Blakeslee ( 2 ) has investigated the sexual condition 
of the spores in Marchantia polymorpha and Fegatella conica , and finds that 
in each of these species the spores from any one capsule give rise to both 
male and female plants. 
It is interesting to note that variations in the sexual condition of 
normally dioecious species have been discovered in the Hepaticae as well as 
in the Musci. In Preissia commutata the occurrence of an androgynous 
receptacle has been described by Townsend ( 17 ), and such organs are not 
infrequently found in this species. The investigations on the Hepaticae 
which have just been described are of the type of that of 6l. and Em. 
Marchal on the Musci, and do not bring forward any direct evidence as to 
the sexual condition of the gametes. 
Investigations carried out on other groups are more numerous in 
number, but it is questionable how far the results obtained are applicable to 
the Bryophyta. 
Strasburger fully discussed the question of sex determination in 
1909 ( 16 ), and concluded that in plants generally each kind of gamete 
bears only the tendency of its own particular sex, i. e. maleness is confined 
to the spermatozoid, and femaleness to the ovum. Correns ( 5 ), on the 
other hand, concludes that in the higher plants and animals the germ-cells 
of one sex are homogametic, while those of the other are heterogametic ; he 
considers that it is probable that the homogametic germ-cells agree in 
sexual tendency with the sex producing them, while of the heterogametic 
germ-cells half bear the tendency of one sex and half of the other. It 
appears, therefore, that considerable difference of opinion exists on this 
point, and that the evidence is not by any means conclusive. 
The results obtained by El. and 6m. Marchal in their experiments 
with the Musci are of great interest, and emphasize the necessity for further 
research. In view, however, of the occurrence of mixed organs in an axis 
of Mnium hornum which has been just described, and the similar cases 
previously noted by investigators in other mosses, together with the work of 
Philibert and Milde, these results cannot be accepted as conclusive of the 
place and method of sex determination in this group ; further research is 
necessary before a definite statement on this subject can be made. 
The supposition that sex determination takes place at some fixed 
stage in the life-history of the plant, and that it is brought about by 
the separation of chromosomes, obviously leads to many difficulties. It is 
therefore suggested that sex is determined by certain metabolic processes 
