44 Finger and Toe, and Wart Disease [CH. 
Wart Disease (Black Scab) of Potatoes (Synchytrium 
endobiotica). 
This disease, which also goes by the name of cauli- 
flower disease, potato tumour, and canker, was intro- 
duced from the continent about 20 years ago. 
Its appearance varies with the virulence of the 
attack. In slight attacks it may not be noticeable or 
may appear as small blackish warts near the eyes. In 
bad attacks large cauliflower-like outgrowths are formed 
on the shoots arising from the tuber. These are at 
first the same colour as the potato, but eventually 
become almost black. The outgrowths always make 
their appearance at the eyes, but later they may 
spread over the tuber. They vary in size and at times 
may be larger than the tuber on which they are borne. 
By taking sections of the outgrowth many of the cells 
may be seen to contain a number of roundish spore-like 
bodies with thick walls. Some of these are said to 
germinate directly but others do not germinate for 
several years. On germination one of these spore-like 
bodies produces a number of zoospores, each carrying 
one flagellum. By means of these zoospores other 
potato plants are infected. When a potato rots they 
are liberated into the soil, and potatoes planted are 
liable to infection. They are said to be capable of 
living for five or six years. The disease also spreads 
from slightly diseased tubers if they are planted the 
following season. It does not attack other crops. It 
is very local and prevails in certain districts in the 
west and north of England, and in Scotland, especially 
