252 Researches into the Nature of the Potato-Fungus. 
morphological relation to Phytophthora. But in several tubers 
which had sprouted in the ground, and were very much collapsed 
in the interior, there was found, not only in the experiments 
made in 1874, but also this summer, in the discoloured tissues 
containing Phytophthora, a form of fungus, the first sight of 
which showed that it must be either a Peronosporea or Sapro- 
legniea, with oogonia, antheridia, and oospores (see Fig. 6.) 
Fig. 6. — Pythium vexans, De Bary. 
1. A mycelinm-tube with two oogonia (a and b) almost matiirc, with antheridia, n. In a the- 
attachments of the oogonium and antheridium are not seen, being behind ; in b, the insertion 
is somewhat oblique. Magn. €00 diam. 2. Germinating oospore sending out mycelivun. 3. The 
same forming zoosfiores. 2 and 3 a little Iffs magnified than 1. 
The suspicion readily suggested itself that the organs of Phyto- 
phthora which had been so long looked for were at last ^found. 
However, in this case a closer examination showed that this was 
a mistake. It will, however, be instructive for my purpose to 
enter here into some details. The presumed oospore-bearing 
fungus was found, as has been said, in the tissues discoloured by 
Phytophtliora, and that, too, in the interior of the cells. Its 
oogonia, in various stages of maturity, were supported in a 
characteristic manner (which I shall more fully describe here- 
after), on cylindrical threads without septa, completely resembling 
in structure those of Phytophthora. though, it is true, distinguished 
by a different distribution of protoplasm, and by being much 
thinner than the usual Phytophthora mycelium. It became, how- 
ever, abundantly clear that these thin threads were branches of 
other mycelium, which corresponded in thickness with the 
mycelium of Phytophthora, and like it, buried themselves among 
the cells of the potato in the intercellular passages. It was- 
