TYPES OF CRYPTOGAMS; 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 
multiplication. 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 afew are good food, and even these contain but little 
nutriment. Some species are dangerous, and a few are deadly 
poisons. The puffballs are a small group allied to the mush- 
rooms. Most of them are edible and of good quality. 
The mildews (Microsphera, etc.) and the “ black-knot ” 
of the plum trees are of a group which likewise includes 
about one-fourth of the fungi. A considerable number 
are parasites, injurious to vegetation, while thousands of 
others grow on dead leaves, twigs, etc. 
