POTATO WART 
383 
Signs of the Disease. — The effects are found in the potato 
itself and not on the parts above ground, which accounts 
for its not being discovered till harvesting time. The first 
evidences of wart are small spongy outgrowths on the sur¬ 
face of the potato, especially at the eyes. Sometimes warts 
arise on different parts of the same potato, transforming 
it into a spongy mass 
which turns from brown, 
the first color, to black, 
and decays (Figure 350). 
What Causes Wart. — 
Wart is caused by a 
fungus which penetrates 
the outer coat of the po¬ 
tato and stimulates the 
cells to abnormal growth. 
When the wart decays, it 
fills the soil with millions 
of sporangia of two sorts, 
one capable of germinat¬ 
ing at once and infect¬ 
ing new potatoes or new 
places on the same po¬ 
tato, and the other rest¬ 
ing sporangia, capable of 
living over the winter and starting the infection anew in 
the spring, or lying dormant for years until conditions be¬ 
come favorable for germination. 
How the Fungus May Be Spread. — (1) By drainage from 
infected fields; (2) by distribution of the infected soil; 
(3) by the use of manure of animals which have eaten the 
raw potatoes; (4) by garbage into which peelings from 
diseased potatoes have been thrown; and (5) by planting 
diseased potatoes or those which have grown in infested 
soil and carry the spores on their surfaces. 
Figure 350 . — Potato Wart. 
