436 Wilson.—Sex Determination in Mnium hornum. 
reusement a travers tout la phase haploidique. . . . L’acte de la fecondation 
reunit a nouveau dans l’ceuf les deux determinants sexuels’ (10, p. 766). 
In an aposporously produced individual it was assumed that no previous 
reduction had taken place, and in a later paper (12) the correctness of this 
assumption is demonstrated, for it is shown that the gametophyte of 
an aposporously produced moss contains the %n number of chromosomes. 
In the absence of meiosis such an individual, according to the theory, 
will be necessarily bisexual, and proof that this is actually the case is 
brought forward by means of numerous cultures (10). 
The proportion of bisexual axes in such cultures is, however, unex¬ 
pectedly small. In the case of Bryum caespiticium , out of 1,738 axes 
examined, 1,579 or 90*8 % were found to be male, 154 or 8*8 % bisexual, and 
5 or 0-28 % female. During the third month of the production of sexual 
organs the proportion of bisexual axes rose to 11*2 % (10, p. 78a). Mnium 
hornum and Bryum argenteum gave almost similar results. 
If there is an absolute separation of sex determinants at the reduction 
division as suggested by El. and Em. Marchal, it would be expected that at 
least a very large proportion of the axes formed on aposporously produced 
protonemata would bear both male and female organs. The results just 
quoted show, however, that this is not the case, and a further explanation 
must evidently be sought for to account for the great preponderance of male 
individuals. It is evident that the proportion is not affected by external 
conditions for, in cultures of dioecious mosses produced from spores, carried 
out by the same investigators ( 9 ) under similar cultural conditions, the 
numbers of male and female individuals were approximately equal; varia¬ 
tions in light intensity, heat, and nutritive conditions had no appreciable 
effect on the proportions of the sexes. 
El. and 6m. Marchal assume that the unisexuality of the plants in 
the aposporously produced cultures is only apparent, and that it hides 
a potential hermaphroditism. Evidence for this is brought forward by 
showing that, in the second aposporous generation, i. e. in plants borne 
on protonemata normally produced from the leaves of the first aposporous 
generation, a small number of synoecious axes is always found, and this pro- 
portion is approximately constant whatever the sexual condition of the 
parent pi a 
The production of protonemata from various parts of the gametophyte 
may be looked upon as a special form of vegetative reproduction, and it 
would be expected that such protonemata would produce axes of similar sex 
to that of the parent. This, indeed, has been shown to be the case by 6 l. 
and Em. Marchal in normally produced individuals ( 9 ). In the case 
of Bryum caespiticium , however, a protonema derived from an aposporously 
produced synoecious axis gave rise to twenty-two axes, of which eighteen or 
8i»8 % were male and four or 18*2 % bisexual. Male and female axes gave 
