236 ELEMENTS OF BOTANY 
of the fungi. A considerable number are parasites, inju- 
rious to vegetation, while thousands of others grow on 
dead leaves, twigs, etc. 
The “rust” of wheat and the “smut” of corn repre- 
sent groups numbering only a few hundreds of species, 
which are very important because they are all parasites 
on living plants, many on our most important economic 
plants. 
Fig. 160, representing another small group of destruc- 
tive parasites, shows clearly how a parasitic fungus grows 
from a spore which has found lodgment in the tissues of 
a leaf and pushes out stalks through the stomata to dis- 
tribute its spores. 
