140 Wager. — Observations on the Structure 
The nuclei in the oosphere, at all stages except the earliest; 
appear to contain very little chromatin, and are very different 
in appearance from the other nuclei. I may, however, point 
out here that observations on the protoplasm and nuclei inside 
the wall of the fully formed oosphere are rendered somewhat 
difficult on account of the thickness of its cell-wall, which 
prevents the proper penetration of the preservative and other 
fluids. To this cause may perhaps be traced the apparent 
absence of chromatin in the nuclei. 
At a late stage in the formation of the oosphere the anthe- 
ridium contains only a very small number of nuclei. It 
appears that some of them pass over into the antheridial tube, 
and then into the periplasm, through the breaking down of 
the swollen end of the tube, which disappears at a later 
stage, the smaller portion of the tube also becoming lost 
to view. 
The outer layer of the wall of the oospore is formed by the 
deposition of the whole remaining mass of protoplasm and 
nuclei upon the inner wall in the form of a rugose mass which 
gradually becomes converted into a dense exosporium. The 
wall of the oogonium at the same time contracts and forms at 
this stage a much crumpled envelope for the oospore. The 
antheridium, which contains a few nuclei, also appears to con- 
tract and finally disappears altogether. 
I should like to call attention here to the observations made 
by Fisch 1 and Chmielewsky 2 on the two genera allied to Pero- 
nospora — Pythium and Cystopus. 
Fisch states that in Pythium the mycelium contains large 
numbers of nuclei, each having a very large nucleolus. The 
young oogonia contain usually from ten to twenty nuclei. At 
the time when the oosphere is being formed, they collect to- 
gether and coalesce into the single large nucleus of the ovum. 
The antheridial cell was found to contain only a single nu- 
cleus, but this was probably formed by the coalescence of 
1 Versamml. deutsch. Naturf. 1885. See Bot. Centrbl., 1885, p. 221. 
2 Arbeiten d. neurussischen Naturf. Ges., xiii, 1888. See Bot. Centrbl., i88_>,- 
No. 24. 
