^ Researches into the Nature of the Potato-Fimgus. 249 
(1875), when the fungus appeared in this district in sad abun- 
dance, I obtained a very large amount of material for study,, 
and at the same time secured the kindly assistance of two 
botanists experienced in researches of this kind, Dr. Rostafinski 
and Dr. Stahl. But again only negative results were arrived at. 
4. From the researches on the tubers it seemed possible that 
by other methods the oospores in the potato might be discovered. 
It is known that in tubers which are well-ripened and compa- 
ratively free from water, the mycelium is capable of living and' 
vegetating for a long time, even until well into the following 
summer. If we cut such tubers and place them in a moist 
atmosphere, the fungus grows luxuriantly from the cut surface, 
and forms stronger conidiophores than anywhere else. In a 
moist atmosphere the fungus will send out conidiophores through 
the skin ; and Kiihn * has called attention to the fact that this- 
phenomenon occurs in cellars without artificial encourage- 
ment. Since then known facts do not exclude the possibility 
of Phytophthora being a Saprolegniea, or, at any rate, being closelj 
allied to Saprolegniece, and since most fungi of this family grow 
in water, while even the few species which are parasitic on 
land plants, fructify most abundantly under water, the question 
arises whether this may not also hold good of the potato-fungus,, 
particularly as regards the formation of oospores. Accordingly, 
tubers with abundance of mycelium were repeatedly placed in: 
spring-water. The invariable result was that numerous branches 
from the mycelium grew in the water. These had the same- 
peculiarities as branches sent out in the moist air ; some even 
assumed the character of conidiophores, forming at the extremity 
conidia, which, without falling off, produced zoospores, re- 
sembling in this respect the sporangium of Saprolegniea;. But 
each time this entire water-vegetation of the Phytophthora 
quickly perished with the corruption of the potato, and not the 
slightest trace of oogonia was found. The same experiment was 
repeatedly made with stalks and leaves, which were filled with 
the fungus, but always without any positive result, because a 
plant which the fungus has attacked at once becomes rotten in 
water, and the Phytophthora dies as soon as the surrounding 
tissues are rotten. 
The experiment was then so far changed by placing the same- 
substances in moist earth instead of in water. From the tubers 
grew up the usual conidiophores ; but here also the stems and 
leaves quickly became rotten, and the fungus with its oogonia 
nowhere occurred. Other forms of fungi, not belonging to 
Phytophthora, were, it need not be said, very often found. 
* Zeitschrift dee landwLrthschaftlichen Central- Vereins d. Provinz SacbseD,. 
1870, No. 12. 
