192 



STUDIES IN CRYPTOGAMS 



355. Leaf of barberry with 

 cluster-cups. 



a cross-section of one of the cups, outlining the long chains of spores, 

 and the mycelium in the tissues. 



The aecidiospores are formed in the spring, and after they have been 

 set free some of them lodge on wheat or other grasses, where they germi- 

 nate immediately. The germ-tube 

 enters the leaf through a stomate, 

 whence it spreads among the cells of 

 the wheat plant. The aecidiospores 

 are not able to infect the barberry 

 leaf. During summer one-celled 

 uredospores ("blight spores") are 

 produced in a manner similar to the 

 teleutospores. The sori bearing them are red, due to the color of the 

 spores of the mass. These are capable of germinating immediately 

 and serve to disseminate the fungus during the summer on other wheat 

 plants or grasses. (Fig. 357.) 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 phenom- 

 enon is called heteroecism, 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 be- 

 tween 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 sowing the aecidiospores 

 on healthy wheat 

 plants and thus pro- 

 ducing the rust. The 

 cedar apple is another 



rust, the fungus producing the curious swellings often 

 found on the branches of red cedar trees. In the spring 

 the teleutospores ooze out from the "apple" in brownish yellow masses. 

 It has been found that these attack various pomaceous fruit trees pro- 

 ducing fficidia on their leaves. Cedar t/ees about orchards may be a 

 menace unless carefully watched. 



356. Section through a cluster-cup on 

 barberry leaf. 



