268 Researclies into the Nature of the Potato-Fungus. 
same time several other diseased tubers also gave off small 
shoots, into which the mycelium of the fungus had passed from 
the tuber ; no further observation, however, was made on them, 
because the disease was then far advanced everywhere. Most 
of the shoots were still quite healthy at their base. They 
could not, therefore, have received the infection from their tubers, 
but it could only have come from the conidia produced on the 
five diseased shoots. To remove all doubts on this point, several 
stocks were entirely dug up and closely examined in all parts. 
Two red kidneys had the old tuber still turgent, and altogether 
free from the fungus ; the base of the shoots was likewise entirely 
free from the fungus, while in the upper part the fungus spots 
existed in abundance. During all this time to the end of May, 
there was nothing remarkable in the weather ; it was, in general, 
moderately moist. The wet weather, under the influence of 
which the fields here suffered so much from Phytophthora, did 
not come till much later ; and at the time when my experiment 
was completed, I did not, in a number of excursions specially 
made for the purpose discover any Phytophthora in the fields. 
The garden in which the experiment was made was in the town, 
far from the fields ; it is to be hoped my experiment was not 
the means of extending the infection to the fields. 
The results I have described having been accurately ascer- 
tained, the problem before us is, as far as possible, solved ; that 
is to say, I have shown that the oospores are not found in this 
district, and that the perennial mycelium discharges the function 
of hibernation which is proper to the oospores in other species. 
I may in a few words draw attention to this fact, that the 
generally known phenomena connected with the occurrence of 
the fungus correspond completely with the result at which I have 
arrived. This may not at first sight appear to be the case, for 
while the first infection of the plants in the fields takes place, 
as we see, in spring, the occurrence of Phytophthora is seldom 
plainly visible before July. But then even in large fields there 
can hardly be more than a few original seats of infection, since 
comparatively few diseased potatoes will be planted, while 
numbers of the diseased tubers actually planted are rendered 
harmless, from the fungus not forming conidia either in tlwm or 
in their shoots. There must be a very large quantity of conidia to 
enable the fungus to spread over extensive areas. A compai'atively 
small quantity only can be produced at first in the primary seat 
of infection. The original development of the fungus, and the 
production of secondary centres of infection, must therefore 
proceed slowly and unnoticed. That is to say, the fungus needs 
time to acquire the quantity of reproductive conidia necessary 
to affect large areas. Were it not so, the potato-plant in damp 
