129 



i^ntiated in a necklace -like manner, and gave birth to the 

 zoospores far removed from the original vesicles. The 

 same thread also produced two true oogonia on the water. 



4. In your last report of the meeting of the Scientific 

 Committee (p. 113, middle column), under Saprolegnia, 

 you say Mr. Renay showed a species of Saprolegnia which 

 might be mistaken for the spores (meaning oogonia) of Pe- 

 ronospora. But if reference is made to my original paper 

 it will be seen from the first that I have perceived the inti- 

 mate connection between the new condition of the Potato 

 fungus and the Saprolegniese. On my side I have the high 

 authority o Thuret and Berkeley for similar alteration in 

 the diseases of silkworms, flies, &c. I am quite prepared, 

 therefore, to consider Mr, Renny's plant the same, or some 

 close ally, with mine, even if it should turn out to be a 

 true Pythium, and its oogonia produce zoospores in water, 

 especially after what is known of the nature of Cystopus, 

 the close ally of Peronospora. Two strong points in favour 

 of this view are these: (1.) The resting-spores of Pythium, 

 are unknoion, but if I find Pythium inside potato stems and 

 leaves mixed up with the Peronospora, and the same Pythium 

 in the very centre of the tuber of the potato (as I have 

 done), there maturing itself and forming its resting- 

 spore, then the identity of the two may reasonably be assum- 

 ed, and the resting.spore of the Pythium, as well as the 

 Peronospora, is found. (2) The same cells in the Sapro- 

 legniese will alternately produce, under the same (or diffi- 

 rent) conditions, zoospores or resting spores, therefore, if 

 zoospores are produced in Mr. Renny's oogonia in water, it 

 is reasonable to assume that under different conditions res- 

 ting-spores would be formed by similar cells. I have, from 

 the first, believed the Saprolegnia condition of the fungus 

 to be widely diffused, and when in that state it quite pos- 

 sibly grows on diverse plants and substances in watery places, 

 as you well explained the subject last week. The Sapro- 

 fegnia is the caterpillar condition (belonging to the water, 



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