288 



GENERAL MORPHOLOGY OF PLANTS 



455. Prevention of wheat rust. No practical method has 

 been fouad of successfully combatting the wheat rust. Formerly 

 laws were enacted in England and Massachusetts requiring the 

 destruction of the barberry, but this did not materially lessen the 

 disease. The selection of resistant varieties gives promise of solv- 

 ing the problem. The " Marconi " wheats are more resistant 

 than many other varieties, and experiments in crossing are being 



Fig. 264. 



Cedar apples after the spring rains begin. The mass of gelatin swollen by the rains 

 is oozing out in strings and carrying with it the teleutospores of the fungus (Gymno- 

 sporangium macropus). 



made with the hope of obtaining still more resistant strains (see 

 paragraph 663). 



456. Cedar apples and cedar rust. " Cedar apples " are 

 galls formed on the leaves and young twigs of the cedar, through 

 the stimulus of the mycelium of one of the rust fungi. These 

 belong to the genus Gymnosporangium. In early spring, the 

 teleutospores formed in the gall the previous year, in little nests, 

 ooze out in strings in wet weather, because of the large amount of 



