72 Plant Life and Evolution 



meadow manured by the animals feeding upon the 

 grass, sends its filaments deep into the rich earth, 

 where they form extensive white root-like fibers 

 which attack the organic matter in the soil much as 

 the mold attacks the starch in the bread. The con- 

 spicuous, umbrella-shaped mushroom is merely the 

 fructification of the plant, most of whose existence 

 is passed under ground. Such fungi as the molds 

 and toadstools, which live upon dead matter, are 

 known as saprophytes. 



Quite different in their habits are the parasitic 

 fungi, which attack living animals and plants, and 

 are the causes of many of the most serious plant 

 diseases. A common animal parasite is the little 

 fungus that often kills house flies in the autumn, 

 and causes the infected insect to stick to a window- 

 pane, where it is surrounded by a halo of tiny spores 

 shot off from the ends of the filaments that protrude 

 from the body of the fly, within which the fungus 

 has finally completed its work of destruction. 



A*familiar vegetable parasite is the mildew which 

 so often appears upon rose leaves, distorting them 

 and covering the diseased area with a gray frost-like 

 film. In this case the parasite lives upon the surface 

 of the host-plant, and simply sends little suckers into 

 the cells, and thus obtains the necessary food. Other 

 parasitic fungi, like the rusts, live within the body 

 of the host-plant, and break through the surface 

 only for the purpose of distributing their spores. 



An examination of the cells of a fungus shows 



