304 PRACTICAL COURSE IN BOTANY 
344. Numbers and variety: — Fungi exceed every other 
class of living organisms both in the number of species and 
of individuals composing them. They include such diverse 
forms as bacteria, molds, rusts, mildews, mushrooms, and 
the like, ranging in size all the way from the giant puffball, 
a foot or more in diameter, to the almost inconceivably 
minute influenza bacillus, of which nearly two thousand 
Fic. 433. — Cephalothecium, a fungus parasitic on rosehips — greatly magnified. 
(From Mo. Botanical Garden Rep’t. Photographed by Hedgcock.) 
million can inhabit a single drop of water without incon- 
venient crowding! 
345. The parasitic habit. — But while their life history 
is obscure and hard to trace, the fungi are, as a class, well 
differentiated by their parasitic habit. They contain no 
chlorophyll, can manufacture no food, and consequently 
have to obtain it ready-made from the tissues of living or 
dead animals and plants. On this account they are active 
agents in the production of disease and decay, especially 
certain of those manifold forms that have been grouped 
