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. 



FIG. 331. Apple attacked by the Bitter Rot Fungus, Glomerella rufomacidans. 



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 332 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; 



