CHAPTER XV 



THE SAC FUNGI (ASCOMYCETES) ; THE LICHENS; 

 THE BASIDIUM FUNGI (BASIDIOMYCETES) 



THE SAC FUNGI (ASCOMYCETES) 



219. General characteristics. More of the fungi belong to 

 this class than to any other, and since most of the ascomycetes 

 are parasitic, it is evident that the class is one of great im- 

 portance. There is wide variation in form and structure in 

 this group. The mycelium of the parasitic forms grows mainly 

 upon instead of within the host, and sends into it short haus- 

 toria which absorb food material. The hyphse of the mycelium 

 are divided into many cells, and branch extensively. Many 

 of the known structures are difficult to understand, and 

 many of the facts are not known regarding the life cycles of 

 some of the plants which belong in this class. In a general 

 way, the fungi of this class are subdivided into two groups, 

 those which have their spore-forming sacs opening into cup- 

 like structures, and those which have the spore sacs inclosed, 

 or almost inclosed, in heavy-walled and more or less spheri- 

 cal cases. Common illustrations of the class are the mildews 

 which grow upon leaves of the plantain, smartweed, and lilac, 

 the cup fungi, the morel, and yeasts. Of the many represent- 

 atives, but a few types will be used to give some general 

 notions of the structure and importance of the class. 



220. Peziza and Sclerotinia. In damp soil, attached to decay- 

 ing sticks or roots, may be found the pink or reddish cup fungus, 

 Peziza. Peziza plants sometimes appear singly and sometimes 

 in clusters or rows, and in color some of them are very striking. 



Growing from old plums and peaches which have shriveled 

 and dried (become mummified), sometimes there are found 

 similar though brownish cups, which contain the reproductive 



226 



