194 



PLANT BIOLOGY 



and serve to disseminate the fungus during the summer on other 

 wheat plants or grasses. Late in the season, teleutospores are 

 again produced, completing the life cycle of the plant. 



Many rusts besides Puccinia graminis produce different spore 

 forms on different plants The phenomenon is called heterxcism, 

 and was first shown to exist in the wheat rust. Curiously enough, 

 the peasants of Europe had observed and asserted that barberry 

 bushes cause wheat to blight long before science explained the 

 relation between the cluster-cups on barberry and the rust on 

 wheat. The true relation was actually demonstrated, as has since 

 been done for many other rusts on their respective hosts, by sow- 

 ing the aecidiospores on healthy wheat plants and thus producing 



FlQ. 285. How A PARASITIC FUNGUS WORKS. Anthracnose on a bean pod 

 entering the bean beneath. (Whetzel.) 



the rust. The cedar apple is another rust, producing the curious 

 swellings often found on the branches of red cedar trees. In the 

 spring the teleutospores ooze out from the " apple " in brown- 

 ish yellow masses. It has been found that these attack various 

 fruit trees, producing aecidia on their leaves. Fig. 285 explains 

 how a parasitic fungus works. 



Puffballs, mushrooms, toadstools, and shelf fungi. These 



represent what are called the higher fungi, because of the size and 



complexity of the plant body as well as from the fact that they 



;em to stand at the end of one line of evolution. The mycelial 



breads grow together in extensive strands in rotten wood or in 



the soil, and send out large complex growths of mycelium in con- 



