934 ELEMENTS OF BOTANY. 
The mycelium of these is generally concealed in the substance 
of the earth, decaying wood, or other material on which the 
fungus grows, and the conspicuous portion of the plant is 
that on which the spores are borne. 
Lichens, familiar objects encrusting rocks or hanging in 
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Fic. 201.—Spore-Formation in Potato Blight (Phytophthora infestans). 
A, an unbranched stalk, proceeding from the mycelium m in the interior of the 
potato leaf, passing out of the epidermis e through the stoma sp, and bearing 
a single spore-case ; B, an older group of stalks, showing spore-cases in various 
stages. (Both greatly magnified, 4 more highly than B.) 
beard-like tufts from the bark of trees, which were once 
regarded as constituting a separate division of the vegetable 
kingdom, are now known to be curious examples of a kind of 
