250 Researches into the Nature of the Potato-Fungus. 
5. After these successive failures, there still remained a 
possible method of discovering the oospores, suggested by 
another phenomenon observed in the tubers. It is known that 
potatoes which are injured and infested with Phytophthora are 
capable of sprouting, like healthy specimens, and even producing 
entirely healthy shoots and plants. While examining diseased 
tubers of this kind which had sprouted, I had often, after they 
were shrivelled, found, in the tissue which contained the Phyto- 
phthora, bodies which, it might be supposed, were oospores of 
a Peronosporea or a Saprolegniea. On the other hand, I had 
observed in several previous experiments with diseased tubers 
a condition of the mycelium which seemed to promise a positive 
result. It is known that the starch contained in the healthy 
colourless tissues of the sprouting tuber is gradually reduced in 
quantity, and that the large cells become filled with watery 
liquid. Owing to this the whole structure becomes watery- 
transparent : it remains at first turgid and firm, then afterwards 
it collapses and decay takes place. In the diseased tubers this 
phenomenon occurs in the tissues which have remained healthy, 
and which are principally found in the centre of the tuber, while 
the fungus generally keeps to the periphery or exterior portion, 
where it discolours and kills the cells. During the sprouting of 
the tuber we can see the fungus shooting from the discoloured 
portion into the watery and healthy centre, where it grows very 
luxuriantly. It sends out many branches between the cells of 
the tuber, and also forces short branches into the interior of the 
cells ; it is vigorous, filled with colourless protoplasm, and gives 
an impression of most exuberant growth. No discoloration of 
the watery-tissues, it should be said, takes place. These pheno- 
mena suggested the possibility that the luxuriant branching of 
the fungus in the sprouting potato was for the purpose of forming 
the oospores. On this hypothesis hinged another ; viz. : that the 
supposed formation of oospores must be completed, and the 
oospores matured, simultaneously with the shrivelling up of the 
seed-tubers. This would, moreover, be about the time of the 
full development of the potato plant, when the fungus usually 
appears in large quantities. Now, it is not absolutely necessary 
that oospores should pass a winter before germination ; the 
germination, as has been stated above in regard to Sapro- 
legniece, may take place speedily after they arrive at maturity ; 
and in the PeronosporecB, it may at least be looked upon as 
a possible phenomenon, depending upon surrounding circum- 
stances. Thus arose the conjectures that perhaps the oospores 
of the potato-fungus originated from the mycelium growing in 
the sprouting tuber ; that the oospores germinate immediately 
after they reach maturity, which is contemporaneous with the full 
