CHAPTER XIV 
PLANT DISEASES 
Plants, like animals, are subject to many diseases, and 
often these are due to similar causes. Infectious diseases, 
such as measles, mumps, and typhoid fever, are produced 
by germs or bacteria that get into a person’s system; and 
practically all cultivated plants are attacked by similar para- 
sites. These live in the body of the plant and feed upon its 
substance, causing the loss of health and sometimes of its 
life. As a farming, gardening, or fruit-growing district 
gets older, each crop becomes more and more liable to at- 
tack by its own particular enemy. These disease-producing 
parasites are low types of plants. Some of them are bacteria, 
but a larger number are fungi (plural of fungus). To enable 
us to understand more clearly the nature of plant diseases, 
we must learn something about the characteristics of bacteria 
and fungi. 
Nature and Causes of Plant Disease.— Bacteria and 
fungi are not green, as the leaves of ordinary plants are, and 
this is a very important fact, for without the green coloring 
matter they are unable to manufacture their own food out 
of the elements taken from the soil and the air as higher 
plants do. They must, therefore, live upon food already 
prepared by higher plants. 
Bacteria are the smallest of all plants — so small that we 
should have to place from 10,000 to 25,000 of them side by 
side to cover a line an inch long. Their form is extremely 
181 
