254 Researches into the Nature of the Potato-Funrjus. 
the oospore, formed itself into a ball, and then quickly divided 
itself, generally into from six to eight portions (the number is 
variable), which, like so many zoospores, rapidly quitted the dis- 
solving gelatinous bladder (Fig. 6, These zoospores resemble 
those of species of Peronospora and Pythium, and of Pliytophthora 
in form, structure, and movement (differing, perhaps, from the 
latter to a small extent in size, but this was not precisely deter- 
mined). Like these they move about a short time in the water, 
after which they become quiet and germinate. Their first tubes 
(" germ-tubes ") remained short and without branching, even for 
several days, in the cultivated specimens which have been de- 
scribed. In two hours after sowing, the first zoospores were 
found, mostly in the drops of water. Their number was usually 
much increased in the hours immediately following. 
Thus were developed young plants (" germ-tubes ") and zoo- 
spores which completely resembled those of the potato-fungus. 
Only one thing was wanting ; but that was, without doubt, the 
chief thing, viz., the proof that what was found really belonged 
to Phytophthora, and not to some other fungus resembling it 
and accompanying it. The proof here required could only be 
obtained by ascertaining if the young plants (" germ-tubes ") and 
zoospores would grow on a suitable nidus or substratum into 
undoubted Phytophthora. There was no need for uncertainty in 
determining this, since sufficient quantities of the zoospores or 
germinating bodies of the oospores could be had, and since the 
conditions attending the development of Phytophthora from its 
spores were known. Accordingly I made numerous sowings of 
the oospores in drops of water on fresh leaves, stalks, and tubers 
of the potato. The formation of the zoospores was easily con- 
firmed in these sowings. But nowhere did the young plants 
(" germ-tubes ") advance beyond the stage of development which 
they reached on the glass, nowhere did they penetrate into the 
interior of the living parts of the plants, and nowhere did they 
develop mycelium. This result, repeatedly confirmed with 
certainty, could mean nothing else than that these oospores did 
not belong to Phytophthora, but to another fungus, which ap- 
parently had entered into the already dead tissues of the tuber 
while it was still in the ground. The facts observed regarding 
this fungus corresponded best with the genus Pythium ; and 
since it did not take possession of the living potato-plant, it 
Wcas to be expected that, like most of the members of this genus, 
it would find its suitable nidus or substratum in dead organic 
bodies. From experience acquired in connection with other 
species of Pythium, I now made sowings on dead animals, by 
placing small fragments — as the legs of flies and newly-killed 
mites — on glasses, in drops of water in which the zoospores of 
