of Peronospora parasitica . 277 
the few observations which I have been able to make, that 
a reduction in the number of chromosomes takes place during 
the mitosis in the oogonium and probably in the antheridium. 
Berlese states that in C. Portulacae the reduction takes place 
on the germination of the zygote; but Stevens says that in 
C. Bliti ‘there is some evidence that makes it appear that 
there is a reduction in the number of chromosomes during the 
first mitosis * in the oogonium. 
It is evident that further investigation is necessary before 
any definite statement can be made as to the reduction of 
chromosomes in the Peronosporeae. 
Summary and Conclusions. 
1. The protoplasm of the oogonium becomes differentiated 
into a central vacuolate ooplasm and a granular homogeneous 
periplasm. 
2. Immediately before this takes place a receptive papilla 
is formed on the oogonium at the place where the antheridium 
is in contact with it. At this spot the wall of the oogonium 
becomes very thin, and it is here that the fertilizing tube of 
the antheridium penetrates the oogonium. 
3. The nuclei of the oogonium and antheridium undergo 
mitosis previous to fertilization. 
4. Soon after the delimitation of the oosphere, a dense 
granular mass appears in the centre of it, which becomes 
converted into a homogeneous, ill-defined body, which stains 
more deeply than the surrounding cytoplasm. This central 
body appears to play some part in bringing the sexual nuclei 
together. 
5. A single nucleus from the periplasm of the oosphere 
travels towards the central body and comes into close contact 
with it. The fertilizing tube of the antheridium also grows 
towards it and discharges a single nucleus, which comes into 
close contact with the female nucleus. 
6. The sexual nuclei do not fuse at once, but remain apart 
for some time and increase in size, probably at the expense 
