276 Wager.—On the Fertilization 
nuclear fusion ; and in this species it is delayed until the 
thick zygote-membrane has been partly formed. 
At the time the fusion takes place the protoplasm of the 
oospore contains numerous oil-drops. These gradually fuse 
together to form a large central oil-globule of weak refringent 
power. The protoplasm fills the space between the oil-drop 
and the membrane. It is a finely granular substance and 
contains, as De Bary 1 pointed out, ‘ a round or elongated 
and perfectly pellucid spot’ close to the membrane on one 
side of the spore. De Bary surmised that this might be 
the nucleus, and this turns out to be correct. The ripe oospore 
of P. parasitica is uninucleate ; the nucleus is found in the 
position indicated by De Bary and is clearly visible in the 
living condition. In all the other species of Peronospora which 
have been examined the ripe zygote is multinucleate, and in 
Cystopus, so far as we know at present, the ripe oospores of all 
species are multinucleate. Whether the zygote of P. para¬ 
sitica becomes multinucleate just before germination takes 
place I do not know, as I have not yet been able to get them 
to germinate. 
The periplasm and periplasmic nuclei remain visible for 
some time but ultimately become transformed into the exo- 
sporium, which is laid down on the surface of the endosporium 
as a coarse network (Fig. 17). The wall of the oogonium 
persists, and as the oospore ripens it becomes much thickened 
and serves as an additional protective layer. 
The phenomena of fertilization in P. parasitica thus de¬ 
scribed conform, in their essential characteristics, with those 
observed in the higher plants and animals, so far as the actual 
fusion of nuclei is concerned ; and it resembles in a striking 
manner the fusion of nuclei in Coleochaete pulvinata de¬ 
scribed by Oltmanns 2 . Unfortunately however it has not 
been possible to arrive at any definite conclusions as to the 
question of chromosome-reduction, but it appears to me, from 
1 Fungi, Eng. Edit., p. 135. 
2 Die Entwickelung der Sexualorgane bei Coleochaete pulvinata. Flora, 
vol. lxxxv, 1898. 
