644 Trow . — The Karyology of Saprolegnia. 
nuclei of the sexual organs, it must be remembered, pass into 
them from the mycelial hyphae. 
Although the difficulty presented by the Saprolegnieae is 
not a real one, it is of special interest to note that, even were 
this the case, the difficulty disappears under the light of the few 
observations already made on the functional character of the 
antheridia. Apogamy certainly must inevitably take place in 
the two species in which there is absolutely no provision for 
fertilization. In the other species, more or less closely related 
to S'. mixta , in which apogamy may take place, antheridia 
are sometimes present ; and after what has been said, we may 
be permitted to believe that fertilization may occur whenever 
antheridia and fertilization-tubes are present until this has 
been proved to be impossible. The Saprolegnieae as a group 
must therefore be no more regarded as apogamous than the 
Characeae, the Vascular Cryptogams, or the Phanerogams, in 
all of which isolated apogamous forms occur. 
It might have been expected that the apogamous oogonia 
investigated would have differed from the others by their 
nuclei not undergoing a reducing division. Weismann, indeed, 
anticipated that this would be the case with the parthenogenetic 
ova of animals. The non-occurrence of the reducing division 
would then have accounted for the power of parthenogenetic 
development. As matters stand, we have to account for this 
by assuming — and there are excellent grounds for such an 
assumption — that the half-chromosome, if not increased to 
a whole-chromosome by the sexual process, can attain to the 
required mass by a process of growth during the resting 
period of the oospore. Since the oospheres and zoospores are 
generally admitted to be homologous organs, this is nearly 
equivalent to the statement that the oospheres simply revert 
to their primitive asexual condition. 
The formation of azygospores in both algal and fungal 
conjugate forms, and the apogamous development of the old 
gametes of Botrydium , which appear to be well authenticated, 
to say nothing of the development of weak plants of Ulothrix 
from gametes which have not succeeded in conjugating, maybe 
