226 FUNGI. 



enced in its culture. According to these opinions, the vegetation 

 of the parasite would be purely accidental, the disease would be 

 independent of it, the parasite would be able frequently even to 

 spare the diseased organs. Others see in the vegetation of the 

 Peronospora the immediate or indirect cause of the various 

 symptoms of the disease ; either that the parasite invades the 

 stalks of the potato, and in destroying them, or, so to speak, in 

 poisoning them, determines a diseased state of the tubercles, or 

 that it introduces itself into all the organs of the plant, and 

 that its vegetation is the immediate cause of all the symptoms 

 of the disease that one meets with in any organ whatever. 

 His observations rigorously proved that the opinions of tlie 

 latter were those only which were well founded. All the altera- 

 tions seen on examining spontaneous individuals are found 

 when the Peronospora is sown in a nourishing plant. The most 

 scrupulous examination demonstrates the most perfect identity 

 between the cultivated and spontaneous individuals as much in 

 the organization of the parasite as in the alteration of the plant 

 that nourishes it. In the experiments that he had made he 

 affirms that he never observed an individual or unhealthy pre- 

 disposition of the nourishing plant. It appeared to him, on the 

 contrary, that the more the plant wa.s healthy, the more the 

 mould prospered. 



We cannot follow him through all the details of the growth 

 and development of the disease, or of his experiments on this 

 and allied species, which resulted in the affirmation that the 

 mould immediately determines the disease of the tubercles as 

 well as that of the leaves, and that the vegetation of the 

 Peronospora alone determines the redoubtable epidemic to which 

 the potato is exposed.* We believe that this same observer 

 is still engaged in a series of observations, with the view, 

 if possible, of suggesting some remedy or mitigation of the 

 disease. 



Dr. Hassall pointed out, many years since, the action of 

 fungous mycelium, when coming in contact with cellular tissue, 



* De Bary, " Memoir on Peronospora, " in " Annalcs des Sci. Nat.' f 



