Researches into the Nature of the Potato-Fungus. 
255 
the fungus were abundant. In this manner I might be able to 
observe step by step the whole of the further development The 
zoospores at once attached themselves in great numbers to these 
fragments, and sent out tubes which developed into splendid 
mycelium, and ramified in the animal substances and in the 
surrounding water. It did not form zoospores, but, on the other 
hand, it formed oospores in the interior of the body of the mites, 
exactly like those found in the cells of the potato. I pass over 
here several other observations which were made at this time, 
because they do not concern the question before us, but I would 
only remark in reference to the Pythium, that it is a species 
which has not hitherto been described, and which I now call 
P. vexans, because it has occupied me for almost the whole of 
two long years. 
Before entirely leaving this department of the subject, I wish 
to record another experiment ; and in this case also, not because 
I gained anything positive toward the solution of our problem, 
but because it shows how carefully one must guard against 
being deceived in investigations of this kind. For the sowing 
of Pythium vexans I had got, beside others (July 20), half-a- 
dozen fresh new potatoes. Externally they looked healthy. One 
was immediately used for experiment and cut in two. I placed 
a sowing of Pythium on the cut surface of the one half ; I did 
not inoculate the other half; each was placed separately under 
a small glass bell in a moist atmosphere. On the next and the 
second day the germination of the Pythium, as described above, 
was confirmed in the inoculated half. But on the third or fourth 
day I was agreeably surprised to find on the inoculated surface 
the beautiful conidiophores of the potato-fungus. 
It is true that they were not growing on the very spot where I 
had sown the Pythium vexans ; still, they were close to it. From 
that point outward to the edge they covered the surface of the 
section, and they also extended down the thin skin of the 
external surface for some distance. In these places mycelium 
was always found in the interior of the tubers. Search was 
made in vain for a connection between it and the young plants 
grown from the sowing of the Pythium. The non-infected half, 
which from the beginning of the experiment had been kept 
quite isolated, also presented, on the same day as the infected 
half, conidiophores of the potato-fungus on its surface. Up to 
this point the other potatoes had been preserved in a different 
place, lying exposed to the dry air of the room. Externally, 
they appeared to be healthy, with the exception of one or two 
dark spots on the surface. They were placed without any arti- 
ficial infection under glass bells in a moist atmosphere, and the 
disease, together with the eruption of conidia, appeared in all of 
