of Peronospora parasitica. 269 
1. Collective nuclear fusion as in Pythium (Fisch). 
2. Binuclear fusion as in Cystopus candidus , C. Portidacae 
and species of Peronospora (Wager and Berlese). 
3. Multiple nuclear fusion, in pairs, as in C. Bliti (Stevens). 
It is probable that the method of fertilization described by 
Fisch for Pythium will be found to be untenable. The second 
type of nuclear fusion has been found to be the most frequent 
in the Peronosporeae, so far; and the third type must be 
regarded therefore, at present, as the anomalous one. 
The observations on P. parasitica which follow show that 
this species comes definitely in the second group. As the 
general structure of the Fungus was described in a previous 
paper I shall confine myself here to a description of the 
sexual organs and the process of fertilization. 
As in Cystopus , the nuclei of the young oogonium of Pero¬ 
nospora parasitica are irregular in shape and the outline of 
the oogonium, before it is cut off from the parent hypha, 
presents a somewhat crumpled appearance; the nuclei are 
often elongated in the direction of the flow of the protoplasm 
into the oogonium as in Cystopus candidus , and as Stevens 
has also shown to be the case in C. Bliti . As soon as the 
partition-wall separating the oogonium from the hypha is 
formed, the oogonium expands and becomes more or less 
spherical; the nuclei at the same time regain their spherical 
shape (Plate XVI, Fig. 1). 
The structure of the nuclei at this stage is simple. They 
possess a nuclear membrane and a granular network, but no 
nucleolus, or if a nucleolus is present it is very small and 
difficult to distinguish from the granules of the network. 
The structure of the nuclei of the antheridium is the same. 
Soon after the delimitation of the oogonium the protoplasm 
exhibits a vacuolar structure; the antheridium becomes 
closely attached to the wall of the oogonium and, as I have 
shown is also the case in Cystopus , a granular mass of 
protoplasm appears just beneath the membrane of the 
oogonium at the place where the fertilizing tube will be 
formed. At this point the wall separating the oogonium from 
