256 Researches into the Nature of the Potato-Fungus. 
them in from two to three da^ s. I had, therefore, been working 
with material which was diseased before I employed it in the 
experiment ; and this need not seem strange when we remember 
that from the middle of July onwards the potato fields of this 
.district had been frightfully destroyed by Phjtophthora. Still, 
the appearance of the conidiophores of the potato-fungus on the 
half of the potato infected with Pythium might have led to a 
serious and disagreeable deception, but for the opportunity of 
checking it just described. 
7. In the tissues of potatoes penetrated with the mycelium 
of Phytoj>ht]iora, there sometimes appear other bodies, which 
might be regarded as oogonia or oospores of the potato-fungus. 
I have several times found them with Pythium vexans in old 
collapsed tubers which had sprouted in the ground, and once 
without Pythium in a living stalk which had been on the 
ground. But they were always restricted to those regions 
which were occupied by the Phytophthora mycelium, and 
always occurred (with one doubtful exception) in the interior 
of the dead cells of the potato. These bodies, when ripe (see 
Fig. 7), have a globular form with a fine muricated surface. 
Fig. 7. Artotrogus hydnosporus, Mont. (?) from fresh specimens. 
12 3 
■5 and 2. From the stem of a potato ; 1875. Magn. 600 diam. 3. Common form, from a diseased 
tuber of 1874. Magn. 400 diam. 
TThe prominences are sharp protuberances of the colourless, 
tolerably thin, external membrane. Within this is enclosed 
a cell, filled with closely packed protoplasm, also of globular 
form, but with a smooth surface, and having the structure of 
a Pythium-oospore, with thin, almost colourless, epispore. The 
globular cells are often considerably smaller than the prickly 
bag which surrounds them, and then they lie loose* in it, 
enclosed in watery liquid. In other specimens this difference 
of size is so slight that the prickly envelope is all but com- 
pletely filled up by the smooth cell. The first of these forms 
in particular greatly reminds one of the oogonium of some 
Saproleyniece (of the genera Saprolegnica and Aphanomyccs), 
which have prickly prominences, and contain a smooth globular 
oospore. In most cases I found these bodies complete, mature, 
and without any distinct indication of their being attached' to 
