BULLETIN OF THE BUSSEY INSTITUTION. 319 
No. 15.— The Potato Rot. By W. G. FAR tow, Assistant 
Professor of Botany in Harvard University. 
Wutte it has been known to botanists for more than twenty-five 
years that the potato rot is caused by the growth of a minute fungus, 
called by Montagne, who first described it, Botrytis, by later writers 
Peronospora infestans, there are certain points in the life history of 
this fungus which have not yet been cleared up,— points which, if 
answered, might suggest to the farmer a means of avoiding, to some 
extent, the occurrence in its worst forms of this unfortunately too 
common epidemic. The object of the present paper is to give to the 
agriculturalist a statement of the condition of our knowledge of the 
habits of the Peronospora infestans, its germination, growth, propaga- 
tion, &c., to state the questions which science has still to answer, and 
the direction in which investigations will have to be made in the future, 
and, finally, as far as is possible, to apply the knowledge which a mi- 
croscopic study of the Peronospora has given us to a consideration of 
the means of avoiding or diminishing the rot. 
It might, perhaps, seem superfluous to recount the symptoms by 
which the disease, the rot, manifests itself, so familiar are they to the 
persons into whose hands this paper is likely to fall. It makes its 
appearance in midsummer in our latitude, usually about the first of 
August, sometimes earlier, oftener a little later. At times its advent 
is so sudden that, within a few hours, the potato fields change from 
green to brown and black, and the plants which, in the morning, gave 
promise of an abundant crop, before night present a mass of decaying 
vegetation, in which are involved not only the leaves and stems, but, 
also, the tubers. ‘The disease occurred in this violent form in 1842, 
and again in 1845, and spread over a good part of the United States 
and the British Provinces, and also destroyed the crop in Great Brit- 
ain, Ireland, Belgium, and parts of Germany and France. The 
greatest injury was done ‘in Nova Scotia, New Brunswick, and Ire- 
land, owing to the fact that, in these countries, the potato was the 
principal crop. Since 1845, the disease has recurred, but never 
with such violence, although during the last year, 1874, the damage 
was considerable. Although public attention was first called to the 
