LICHENS 379 
from a single cell, as in Yeast, to a massive mycelium which in 
some cases takes no definite shape while in others it forms a 
definitely shaped fruiting body. In parasitic forms the mycelium 
sometimes runs through the tissues of the hosts, and sometimes 
is chiefly superficial, sending only haustoria into the host. 
Fic. 331. — Apple attacked by the Bitter Rot Fungus, Glomerella rufomaculans. 
After Alwood. 
The spores are of two kinds, conidiospores and ascospores. 
The conidiospores are borne free on projecting hyphae, and grow 
directly into hyphae upon germination. The ascospores, the 
characteristic spores of the group, are borne in asci which are 
usually produced within a fruiting body or ascocarp, which may 
be an open structure or a closed one. 
In controlling the disease-producing forms one must reckon 
with conidiospores and ascospores. 
Lichens 
Lichens are very common structures which form splotches on 
stumps, tree trunks, rocks, old boards, etc., and some grow upon 
the ground. Figure 3382 shows an Apple twig covered with 
Lichens. They may appear as a crust covering the support; or 
they may have flat lobed bodies like the one shown in Figure 333; 
