256 PRACTICAL BOTANY 



ascomycetes are of great importance in relation to dairy indus- 

 tries, fermentation, and to diseases of economic plants. 



Basidiomycetes comprise extremely diversified forms, many 

 of which (smuts and rusts) are not conspicuous except in 

 their spore formation. Striking polymorphic life cycles are 

 shown in the rusts. The rusts and smuts are destructive para- 

 sites of the greatest importance. The toadstools and mush- 

 rooms, though representing a very large number of forms with 

 world-wide distribution, have a comparatively simple life cycle. 

 They are chiefly saprophytic, though several forms, as the 

 tree-destroying fungi and others, attack living hosts. Puff- 

 balls are almost exclusively soil saprophytes. 



The lichens exhibit a remarkable case of mutualism or of 

 slavery in which algae and fungi live together in such a way 

 as to compose a new organism. In these organisms the algae 

 do the necessary chlorophyll work, and the fungi, it seems, 

 protect the whole organism, thus making life possible in places 

 and under conditions that would otherwise be impossible for 

 both mutualists. Algae and fungi of the lichen combination 

 reproduce themselves in the ways that are peculiar to the algae 

 and fungi, and not as a new lichen organism. 



240. Classification 



Thallophytes 

 Algae 

 Fungi 



Class I. Phycomycetes 



Class II. Ascomycetes. Leading genera used as illustrations, 



Peziza (cup fungus), Sclerotinia (brown rot), Microsphcera 



(lilac mildew), Morchella (morel), Penicilliinn (blue mold), 



Saccharomyces (yeast), Claviceps (ergot), etc. 



Class III. Lichens. Leading genera used as illustrations, 



Parmelia, Usnea (bearded moss), Cladonia, etc. 

 Class IV. Basidiomycetes. Leading genera used as illustra- 

 tions, Ustilayo (smut), Puccinia (rust), Uromyces (rust), 

 Gymnosporangium (cedar apple), Agaricus, Polyporus, Hydnum 

 (toadstools or mushrooms), Lycoperdon (puft'ball), etc. 



