Researches into the Nature of the Potato-Fungus. 
253 
scarcely possible, especially in the discoloured tissues, to draw a 
positive distinction between the two kinds of intercellular 
filaments. 
The oogonia (1, a, 5) are round cells. Their position on the 
mycelium is either sessile on its outside, or they are inserted 
with a broad base into the mycelium-tube. In contact with the 
oogonium lies an antheridium — rarely two — which, as a rule, is 
club-shaped, and rises close to the oogonium from the same tube 
(1, 7j). Unimportant exceptions to this rule may here be passed 
over. A single oospore is formed from the whole of the pro- 
toplasm of the oogonium. It occupies the cavity, is nearly 
globular, and at the period of maturity has the usual oospore 
structure described above, with very thin, smooth episporium, 
which when mature is of a light yellowish-brown colour, like 
the persistent wall of the oogonium. In the proper place, and 
at the very time when they were sought for, there were, then, 
found oospores which might have belonged to Pliytophtliora 
infestans, not only from their structure, but also because they 
seemed to spring from thin branches of the intercellular myce- 
lium of that fungus. They differed from all similar organisms 
which I knew, in their small size, and in the peculiar insertion 
of the oogonium and antheridium. To test the value of the 
conjecture that these were the oospores of Phytophthora, an 
attempt was made to obtain their speedy germination. To 
observe this, thin slices from one of the potatoes in which they 
were particularly plentiful, but in which other fungi and in- 
fusoria were relatively scarce, were placed in drops of water on 
object-glasses, and the oospores were further isolated. Some 
of the oospores sown in this way germinated, sending out, within 
twenty-four hours, a tube, which became several times longer 
than the diameter of the oogonium (Fig. 6, ^) ; in the course of 
one to two days some of these tubes also sent out several short 
branches, and then they ceased to grow. Previous to this, the 
extremity of the tube or of a branch often swelled into a round 
bladder, into which all the protoplasm was collected, and which 
was then cut off by a septum. The young plant did not grow 
further. When the potatoes which were experimented on had 
been kept a few days longer in a moist atmosphere, so as to 
prevent their drying up, and secure the complete maturity of 
the oospores, new sowings were made. In this case the result 
was different. Some of the oospores did not germinate ; but a 
large number of others speedily sent out a thick, short, straight 
tube, which grew to about the length of the diameter of the 
oospore, and then its further growth lengthwise ceased ; but soon 
its extremity suddenly swelled out into a globular bladder. Into 
this, while it was swelling out, streamed all the protoplasm of 
