Plants as Affected by Fungous Parasites. 165 
attacked by broom rape, as potatoes, Indian corn, beans, 
grains or grasses. In infested crops, the broom rape should 
not be permitted to mature its seeds. 
320. The Dodder of Clover and Flax,* are most in- 
jurious of their class. The young plantlet attaches itself to 
the stem of its host, about which it twines, robbing it of 
nourishment by means of its little suckers. 
Preventives. The seeds of dodder are somewhat smaller 
than those of clover or flax, and hence may be separated 
from the latter by careful sifting. Badly infested ground 
should be devoted for two to four years to a crop not at- 
tacked by the dodder. 
b— Plants as affected by fungous parasites. 
321. The Fungi constitute an extensive class of plants 
that derive their nourishment wholly from organic 
matter. Many of them are injurious to cultivated 
plants. Unlike the harmful insects, most of which work 
their ravages within full view, the fungi are, in very many 
cases, discernible only with the microscope, and reveal their 
presence only by the death or injury of their host. The 
fungous parasites are very numerous and exhibit great di- 
versity of structure and habit. Some of them live only upon 
enfeebled plants, while others attack perfectly healthy ones. 
Some, as the pea mildew, grow upon the surface of their 
host, drawing their nourishment through the epidermis; 
others, like the peach curl and oat smut, grow within the 
tissues of the plant upon which they feed. All of the latter 
class send their fruiting parts to the surface of the host 
plants to disseminate their myriads of spores in the open air. 
* Cuscuta trifolia, C. Epilinum. 
