Trow. — The Karyology of Saprolegnia. 641 
as is well known, the wall of the oospore becomes thinner 
and more permeable to reagents, and the fatty mass disappears. 
A germ-tube is generally produced, and finally a club-shaped 
sporangium is formed. No case of the formation of a germ- 
tube was noticed in the fresh material, the swollen oospore 
itself becoming the sporangium. Moreover, the zoospores 
appeared, as a rule, to remain unliberated and to undergo 
germination inside the sporangium. This mode of develop- 
ment is not infrequent in the normal sporangia of old or 
somewhat unhealthy cultures. 
The material thus obtained was sectioned, and very beautiful 
preparations were the result. While the wall of the oospore is 
still of considerable thickness, and the protoplasm still takes on 
that peculiar reddish tinge with the gentian-violet and eosin 
which I had already found to characterize the resting oospore, 
the oospore contains one nucleus only. This nucleus has the 
same structure — the typical vegetative structure — as those of 
the zoospores, mycelium and sporangia, as is shown in Fig. 24. 
In Fig. 25 we see a binucleate oospore with the nuclei still 
near to each other. The divisions appear to be in all cases 
direct. Figs. 26, 27 and 28 represent oospores with 5, 6 
and 8 nuclei respectively. In these successive stages of 
development it will be noted that there is a gradual thinning 
of the wall of the oospore, an increase in its size, and the 
formation of a central vacuole and zoospore-rudiments, while 
the nuclei undergo division. Fig. 29 represents a section of 
an oospore which had produced 11 zoospores not yet 
entirely separated one from the other. Ultimately we find 
in the cavity of the oospore from 8 to 12 zoospores in 
various stages of germination. I have seen zoospores with 
from 1 to 5 nuclei and germ-tubes of various lengths. In 
the case of one oospore, represented in Fig. 30, which pos- 
sessed 12 nuclei and was the only oospore in the oogonium, 
a germ-tube was produced, no doubt with a view to the 
formation of the typical club-shaped sporangium. 
The uninucleate character of the oospore at the commence- 
ment of germination and its subsequent behaviour finally 
