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 secidiospores 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 secidiospores 

 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 hetercecism, 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 eecidiospores 

 on healthy wheat 

 plants and thus pro- 

 ducing the rust. The 

 cedar apple is another 



357. 



Uredospores of 

 wheat rust. 



356. Section through a cluster-cup on 

 barberry leaf. 



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 aecidia on their leaves. Cedar trees about orchards may be a 

 menace unless carefully watched. 



