139 



The Potato Disease. 

 Translated from Professor de Bary's Monograph op Pero- 



NOSPORA IN " AnNALES DES SCIENCES NatURELLES." 



It is known that the epidemic disease of the potato which has 

 appeared in Europe since 1842, and particularly in 1845, is traced 

 to the presence of Peronospora vifesta?is, a sj^ecies that was dis- 

 covered by Mdme. Libert, and by Montagne. Many authors have 

 treated this malady from different points of view, and it is particu- 

 larly the relations of the parasite with the disease that have been 

 the object of numerous discussions and controversies. In a work 

 treating of Peroiiospora this important subject cannot be passed in 

 silence. The various opinions that have been held upon this sub- 

 ject are so generally known, that it would be useless to give a 

 detailed exposition here. I shall limit myself, then, to a resume, 

 and a criticism that supports itself directly upon observation. 



The opinions classify themselves in two opposite groups. One 

 sees the cause of the epidemic in the diseased state of the potato 

 itself, produced either accidentally by unfavourable conditions of 

 soil and atmosphere, or by a depravation that the plant has ex- 

 perienced in its culture. According to these opinions, the vegeta- 

 tion 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. 



The others see in the vegetation of the Peronospora the imme- 

 diate or indirect cause of the various symptoms of the disease ; 

 either that the parasite invades th-e stalks of the potato, and in 

 destroying them, or, so to speak, in poisoning them, determines a 

 diseased state of the tubers; 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. 



The observations rigorously prove that the opinions of the second 

 group, expressed especially by M. Payen, Montagne, Tulasne, 

 Berkeley, &c., are the only well founded. I can only confirm the 

 theory that one owes to the happy experiments of Dr. Speer- 



