214 BOARD OF AGRICULTURE. 



at all, so that it has been regardecl as a water plant, and so located 

 by the botanists. 



This much of the history of the potato-rot fungus has been known 

 since the investioations of DeBarv in 1SG3. As this disease of the 

 potato makes its appearance in midsummer and runs its course on 

 the tops in a field of potatoes in a few da^'s or a week, and as the 

 spores and mycelium thus far described are destroyed by the frosts 

 of winter, the question arises, how does the fungus continue, or what 

 is the natural state of the fungus during all the rest of the 3-ear? 



There have already been described some eighteen different species 

 of the genus Peronospora, six or seven of which have been observed 

 in this country. Now the complete round of life of quite a number 

 of these species has been clearly made out and is well known. 

 They are multiplied not only b}' spores like those already' described, 

 the conidia and zoospores, but there was also found, entirelv within 

 the tissues of the host plant anotiier kind of a spore which formed a 

 dense, hard, rough outer coating sufficient to protect it from the 

 frosts of winter, and this was called the oospore or resting spore 

 because it was the stage in which the parasite rested from its activit}' 

 during so great a portion of the year. Analogy led us to suppose 

 that there must be a resting spore formed somewhere, which would 

 preserve the life of the potato-rot fungus during its long })eriod of 

 inactivity, and protect it during the freezing cold of winter. For 

 years botanists had been searching for this resting spore, well- 

 knowing that until it was discovered, all attemi)ts to hold the pest 

 in check were just as likel}- to favor the continuance of the fungus 

 as to destro}' it. It is true that Dr. Montague in 1844 found some 

 peculiar bodies in rotten potatoes, which Mr. Berkley claimed were 

 the resting spores, but though searched for again and again, no one 

 was able to find anything like them, and it came to be doubted 

 whether the .bodies described by Dr. Montague under the name of 

 Artotrogus hydnosporus, Mont., had any connection whatever with 

 the potato-rot fungus. It was also well known that certain species 

 of minute parasitic fungi pass one stage of their existence on one 

 species of plant, and another on a totally different species, as the 

 too common rust of wheat which passes one stage on the Bnrberr}' 

 and another on some species of the grass family. 



The so called lettuce mold {Peronospora gangh'/ormis, Berk.) a 

 species closely related to the potato-rot fungus, w^as known to 

 develop in the tissues of lettuce and forjn conidia and zoospores on 



