CHAPTER XVI 
FUNGI AND FUNGOUS DISEASES OF PLANTS 
220. The fungi as dependent plants. In our earlier discus- 
sion of plant nutrition it was found that green plants possess 
chlorophyll, by means of which they make their own foods. 
Every observant person who has had any considerable experi- 
ence with plants has noted several or many kinds, as mush- 
rooms and molds, that do not 
: | Nes possess chlorophyll. These 
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chlorophyll-less plants can- 
not manufacture foods from 
water and carbon dioxide, and 
hence are dependent. Their 
dependence appears in various 
relations between them and 
the host plants or animals 
that supply them the requi- 
site food. Sometimes they live 
upon or within living plants 
or animals, bemg known as 
parasites ; or they may live 
upon dead nutrient sub- 
stances, when they are known 
as saprophytes (fig. 182). 
There are many common fungous parasites, as wheat rust, 
potato blight, and tree-destroying fungi. Our economic crops 
are greatly reduced in value every year through the destruc- 
tiveness of these parasitic plants. Fungous saprophytes are 
also very abundant, the best-known being molds, mushrooms, 
and puffballs. In almost any deeply shaded, moist, and warm 
23d 
< 
Fie. 182. An old pine stump upon 
which the fungus Polyporus is growing 
