CHAPTER III 
DISEASES DUE TO FUNGI 
THE fungi comprise a big group of plants which do not 
possess the green colouring matter common to flowering 
plants generally. They are thus unable to manufacture 
the carbohydrate part of the food from the atmosphere, 
and are dependent upon organic material for their food. 
Some of them live upon dead vegetable matter and are 
called saprophytes, but most of the plant disease organ- 
isms are parasites and obtain their food from the living 
plant. The most successful plant parasites, however, 
are able to exist upon dead vegetable matter when no 
living tissues are available. They thus live upon decaying 
plant remains during the winter, but retain their ability 
to attack and destroy the living plant when such is 
available. 
Instead of developing stem, leaves, and roots in the 
way the higher plants do, the fungi produce tiny thread- 
like structures called hyphe. The hyphe intertwine 
and spread in all directions, and by continued growth 
produce a weft or mat-like mass called the mycelium. 
The hyphe penetrate the plant tissues, through which . 
they ramify and produce the spots, cankers, or other 
lesions typical of the particular disease. Certain threads 
of the mycelium grow up clear of the substratum and 
cut off small bodies called spores. These have thin walls, | 
and being very light are suitable for quick distribution 
and immediate infection of neighbouring plants. They 
are unable to withstand abnormal conditions, and are 
often called “summer ”’ spores. Frequently other spores 
with thick, dark walls are produced, called chlamydo- 
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