TYPES OF CEYPTOGAMS; THALLOPHYTES 275 



333. Occurrence and Mode of Life of Fungi. — Among 

 the most important cryptogamous plants are those which, 

 like the bacteria of consumption, of diphtheria, of typhoid 

 fever, or of cholera, produce disease in man or in the 

 lower animals. The subclass which includes these plants 

 is known by the name Bacteria. Bacteria are now classed 

 by some as a separate group, lower than fungi. Some of 

 the most notable characteristics of these plants are their 

 extreme minuteness and their extraordinary power of 

 jaultiplication. Many bacteria are on the whole highly 

 useful to man, as is the case with those which produce 

 decay in the tissues of dead plants or animals, since these 

 substances would, if it were not for the destructive action 

 of the bacteria of putrefaction and fermentation, remain 

 indefinitely after death to cumber the earth and lock up 

 proteid and other food needed by new organisms. 



The mushrooms and their allies include about one-fourth 

 of the fungi. Some, such as the " dry-rot " fungus, mis- 

 takenly so called, cause great destruction to living and 

 dead tree trunks and timber in economic use. The com- 

 mon mushroom, Agaricus campestris, is the most important 

 edible species. Probably five hundred kinds can be eaten, 

 but only a few are good food, and even these contain but little 

 nutriment. Some species are dangerous, and a few are deadly 

 poisons. The puff balls are a small group allied to the mush- 

 rooms. Most of them are edible and of good quality. 



The mildews (Microsphcera, etc.) and the " black-knot " 

 of the plum trees are of a group which likewise includes 

 about one-fouxth of the fungi. A considerable number 

 are parasites, injurious to vegetation, while thousands of 

 others grow on dead leaves, twigs, etc. 



