Researches into the Nature of the Potato- Fungus. 251 
development of the foliage ; and that their germs at once attack 
the foliage. The difficulty in the way of accepting this theory, 
namely, that the tuber is under while the foliage is above the 
ground, is easily set aside when we remember that the sprouting 
tuber is almost always sought after by minute animals — Acarus, 
Julus, and Lumbricus — by whose agency the oospores could 
readily be brought to the surface of the soil. 
I must begin by saying that the researches made for the 
purpose of testing these theories have also been followed by 
purely negative results. Still it will noi. be useless if I describe 
briefly the various steps of the experiments. 
At the end of February and beginning of March a considerable 
number of potatoes, up to then healthy, were artificially inocu- 
lated, varieties being selected which were known to have re- 
mained a long time watery-turgescent after sprouting. The 
inoculation took place in this way : fresh conidia, capable of 
germinating, were placed on the terminal eyes of the tuber ; the 
infected spot was then covered with a piece of wet blotting-paper, 
and the tubers were placed in a moist atmosphere (under a glass 
bell), out of which they were not taken for several days. By 
this process infection can be obtained with great certainty ; the 
existence of the fungus is, after some time, clearly visible exter- 
nally by the browning of the eyes and the sinking of the 
surrounding parts. In continuing the experiment, only those 
tubers were made use of in which infection had actually taken 
place — about sixty in number, — and the microscopic examina- 
tion which followed invariably disclosed the presence of the 
fungus in their interior. At the end of March and beginning 
of April they were planted partly in flower-pots and partly 
in the open ground. From the eyes, which -remained healthy, 
they sent out many shoots, mostly healthy, but also some 
affected by the fungus, which will afterwards be described. 
They were examined one by one, according to their different 
stages, the last on the 5th of July, with the result that the phe- 
nomena already described presented themselves successively 
in the interior. Oospores were not found. Other fungi, not 
belonging to Phytophthora, were often found growing abundantly 
in the collapsing watery-tissues ; animals of the kinds already 
mentioned and infusoria were also observed. 
6. A great abundance of fungi was developed in the tissues 
of the outer portion of the potato, which are known to resist 
decay very long, but which were discoloured by Phytophtkora. 
The fungi were developed while the tubers were still in the 
ground. These fungi were chiefly of the kinds that have long 
been known to attack sickly tubers, such as Fusisporium and 
Spicaria; it has also been long known that these have no 
