of Peronospora parasitica. 275 
cell (Fig. 9). In this position they become more deeply 
stainable, and consequently more conspicuous. Their structure 
exhibits a granular network, with deeply stained granules, 
and in the later stages a nucleolus can be made out. 
Meanwhile the wall of the oospore, which was beginning 
to form just at the time of fertilization, has been increasing 
in thickness and forms now a very definite membrane, sur¬ 
rounded by the periplasm and the rest of the oogonial 
nuclei. The protoplasmic contents lose their fine vacuolate 
structure. The vacuoles decrease in number and increase 
in size. They mark the position of the large oil-drops which 
are seen in the living oospore. The cytoplasm at this stage 
stains less intensely than before, but the two nuclei, which 
are now very conspicuous objects in the cell, stain more deeply, 
having apparently taken up the stainable substances of the 
cytoplasm. 
The fusion of the two nuclei now takes place (Figs. 10-15). 
They gradually approach again and come into close contact. 
The wall between them breaks down and the contents of the 
two nuclei fuse together. First they are dumb-bell shaped, 
then oval, and finally, when the fusion is complete, spherical 
(Fig. 16). The nucleoli remain distinct until the fusion is 
nearly completed, they then fuse together to form a single 
conspicuous nucleolus which stains deeply. The fusion defin¬ 
itely takes place in the resting stage of the nuclei; there is 
no indication whatever of chromosomes, as figured by Berlese 
in P. Alsinearum and P. effusa. 
The retarded nuclear fusion just described is not uncommon. 
It may occur in the zygotes of Spirogyra , Cosmarium , Clos- 
terium , Basidiobolus , and Polyphagus , and, in some cases, may 
even not take place until germination has commenced. 
In the Peronosporeae we have the two types of fusion. In 
C. candidus , as I have shown, the nuclei fuse at once, im¬ 
mediately after the entry of the male nucleus into the oosphere, 
and the same thing also occurs in C. Portulacae , P. Ficariae , 
P. Alsinearum and P. effusa according to Berlese. P. parasitica 
is at present the only member of the group with retarded 
U 
