1] Introduction to Fungi 17 
life history, such as the times and methods of entering 
the plant, the times and methods of reproduction and 
the plants on which it is capable of living. From these 
data we may be able to find weak spots at which we 
can successfully get the upper hand or prevent it from 
spreading to other plants. Without such knowledge 
we may be attacking the fungus at the period when it 
is least vulnerable. 
CHAPTER II 
POTATO DISEASE AND ALLIED DISEASES 
Potato disease (Phytophthora infestans). 
We must not gather from the name of this disease 
that it is the only one from which the potato plant 
suffers. Potatoes are subject to a number of diseases 
but this one is so called because it is very widespread, 
occurs in all parts of the world where potatoes are 
grown, and because it does the greatest amount of 
damage. It has other names such as potato mildew, 
potato blight, late blight of potatoes, and dry rot of 
potatoes. July is the month to look for signs of the 
disease. The first indication of its presence is the 
appearance of brown patches on the leaves. These 
may appear on any part of the leaf, but are usually 
found at the tips or edges (see Fig. 8). On the under 
surface of these brown patches a pocket lens reveals— 
near the healthy part of the leaf—a number of white 
threads like those of the moulds on bread. Further 
Pp. FB, 2 
