324 DISEASES OF FIELD & GARDEN CROPS. [CH. 



haulm to one side as not dissimilar in its aim and results 

 from the common practice of removing it altogether. In 

 both instances it reduces the yield of large tubers, and at 

 the same time, as we think, has a tendency to prevent 

 the mycelium of the potato fungus reaching the tubers 

 by the inside of the haulm. 



Every one who has experimented with potatoes knows 

 that it is possible to infect tubers with the disease from 

 the spores produced on the leaves. This infection is more 

 readily produced in the eyes where the skin or bark of the 

 tuber is thin and delicate. Infection, however, from the 

 outside of the tuber inwards, is the exception and not 

 the rule. From our own experience, we believe the 

 disease generally reaches the tubers by travelling down 

 the interior of the stem, and that in the majority of in- 

 stances the interior of the tuber is the first part affected, 

 and the disease then works from the inside outwards. 



It commonly happens that potatoes are harvested in 

 an apparently sound condition, but during the winter or 

 early spring the stored tubers are destroyed by the fungus 

 of the murrain bursting through the skin or bark from 

 the inside to the outside. It is also a fact of common obser- 

 vation that when a large number of apparently sound 

 potatoes are cut for seed, disease patches, either large or 

 small, may be seen in the central parts of the tuber, with 

 no apparent connection with the sound parts outside. At 

 the beginning of January 1884 we received a letter from 

 one of the largest potato dealers in this country, com- 

 plaining of a large crop of unsalable potatoes ; the tubers 

 were apparently perfectly sound outside, but full of disease 

 within. A selection of the tubers was also sent on for 

 our inspection, and the sharpest searching failed to detect 

 any disease patches outside ; the interiors of the tubers, 

 on the contrary, were full of dark-brown corroded mur- 

 rain patches. In this bad case, and we know of very 

 many similar ones, it seems impossible that the disease 

 could have been derived through the bark of the tuber, 



