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 



Fig. 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 thej^ are active 

 agents in the production of disease and decay, especially 

 certain of those manifold forms that have been grouped 



