of Peronospora parasitica. 273 
didtis soon after fertilization, as Swingle has also shown 1 , 
and in C. Bliti it reaches its maximum development when 
the daughter-nuclei of the first mitosis pass into the oosphere, 
but disappears before fertilization takes place 2 . In P. para- 
sitica , as in C. Candidas , it attains its highest development at 
the time when fertilization is just about to take place (Fig. 6); 
after fertilization it begins to degenerate, and finally dis¬ 
appears (Figs. 8, 9). That it is not concerned actually in 
the fusion of the sexual nuclei, but only in bringing them 
together, is indicated by the fact that in P.parasitica, although 
it is present when the nuclei come together for the first time, 
it has completely disappeared before fusion takes place 
(Figs. 9-14). In C. Candidas , where the nuclear fusion takes 
place immediately after the male nucleus enters the oosphere, 
the coenocentrum does not entirely disappear until the fusion 
is complete. All the evidence therefore before us, as to the 
function of this structure, indicates that it is functional in 
bringing the sexual nuclei together; and from the fact that 
in P. parasitica the female pro-nucleus becomes elongated 
in the direction of the coenocentrum, as it passes towards it 
through the oosphere (Fig. 4), and that the fertilizing tube 
may grow directly towards it (Fig. 7), it appears that it may 
exert an attractive force of some kind by which the sexual 
nuclei are brought into contact, and that as soon as this has 
been accomplished it begins to disappear. 
As soon as this central body has made its appearance, 
one of the nuclei from the periplasmic layer comes into close 
contact with it (Figs. 4-7). This is the female pro-nucleus. 
In my former paper I stated that this nucleus was formed 
by the fusion of two nuclei, but this is not supported by my 
recent observations, and I suspect that I was misled by the 
coenocentrum, which at this stage looks very much like a 
nucleus, especially in badly stained specimens. This nucleus 
becomes elongated in the direction of the coenocentrum as it 
passes through the cytoplasm, and when it reaches the coeno¬ 
centrum it is often spindle-shaped or fusiform (Fig. 4). Even 
1 Swingle, loc. cit. 2 Stevens, loc. cit, p. 162. 
