594 Wager . — The Sexuality of the Fungi . 
One explanation which seems to me possible is that it is 
brought about by the subsequent development of the oospore 
into an ascogonial filament of cells instead of being simply 
transformed into an ascus, as in Eremascus , and that the 
energy imported by the sexual fusion having become used up 
in the production of the ascogonial cells, the necessary energy 
to produce another reproductive cell, the ascus, can only 
be obtained by a further nuclear fusion. 
In the higher Ascomycetes this second nuclear fusion has 
probably replaced altogether the morphologically sexual 
fusion of the simpler forms, and cannot therefore be regarded 
as a true sexual phenomenon, though perhaps, as Groom 1 
points out, presenting some analogy to the sexual process, 
but not homologous with it. 
The only phenomenon which bears directly upon this 
double fusion of nuclei in the Ascomycetes is that described 
by Chmielewskij in Spirogyra crass a 2 . In this Alga the 
two sexual nuclei fuse together in the zygote ; the resulting 
nucleus then divides, by karyokinetic division, into four, of 
which two break up into fragments and disappear, while the 
other two, the secondary nuclei, again unite into the definite 
nucleus of the zygote, which remains till germination. 
If the phenomenon, as described by Chmielewskij, really 
takes place, it resembles in a striking manner what occurs 
in Sphaerotheca. For in both cases we have first a fusion 
of sexual nuclei, then division into four or more, and sub- 
sequent fusion of two of this again into a single nucleus. 
Looked upon in this light, the second nuclear fusion would 
then be a sexual phenomenon in Sphaerotheca , equivalent to 
the second fusion in the zygote of Spirogyra. And it is 
conceivable, I think, that an equivalent of this second fusion 
may have replaced altogether the primary fusion, so that 
in the higher Ascomycetes the second is the only one which 
1 Groom, On the Fusion of Nuclei among Plants : A Hypothesis. Trans, and 
Proceedings of the Botanical Society of Edinburgh, 1898, p. 132. 
2 Chmielewskij, Materialien zur Morphologie und Physiologie des Sexual- 
processes bei den niederen Pflanzen. Charkow, 1890 (Russisch), Referat in Bot. 
Centralbl., 1 , 1892, p. 264. 
