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ospora infestans), which attacks the potato plant 

 whilst growing, and, having established itself in it, 

 spreads to all parts of the plant, setting up decay 

 wherever it goes. The tubers are not exempt, and 

 when it reaches them putrefactive decay is set up, 

 which often causes them to rot at once, and at any 

 rate spoils those portions of them which it reaches so 

 that they are unfit for culinary purposes. 



Appearance of the Disease, 



The appearance of the disease when a crop is 

 attacked is unfortunately too well known to require 

 much description ; the leaves turn brown, and later on 

 a strong putrid odour is recognisable even at a distance. 

 If a plant is examined in the early stages of the disease 

 small brown spots are noticeable about the leaf and 

 stem, and unless these are carefully observed there is 

 nothing to show that they are not dying in the ordinary 

 course of nature. Closer inspection, however, reveals 

 the presence of a greyish line of mould just where 

 the green and brown portions of the leaf unite, 

 especially on the under side of the leaf. This edging 

 is in reality a streak of mould very similar, to the naked 

 eye, to the mould which is noticeable on decaying 

 vegetables, cheese, old boots, and other familiar 

 substances. The mould has a powdery appearance, 

 but if it is looked at under a magnifying glass it will 

 be seen that it is composed of an immense number of 

 fine threads which occasionally branch, and that they 

 carry small ovoid fruits called conidia. These branches, 



