TYPES OF CRYPTOGAMS; THALLOPHYTES 235 
to be classed with animals as consumers rather than as 
producers, acting on the whole to diminish rather than to 
increase the total amount of organic material on the earth. 
304. 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, Psalliota 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 puffballs are a small group allied 
to the mushrooms. Most of them are edible and of good 
quality. 
The mildews and the “black-knot” of the plum trees 
are of a group which likewise includes about one-fourth 
