310 Diseases of Economic Plants 



brown rings, outside of which is the ordinary green of the 

 healthy leaf. As the spots age they f requentl}^ grow together 

 and form one large oblong area, sometimes several centi- 

 meters long. At a late period in the development of the 

 disease the centers of the spots are occupied by small black 

 specks, the black acervuli of the causal fungus. 



TEOSINTE. See p. 283. 



WHEAT, SPELT, EMMER, EINKORN 



Black-stem-rust {Puccinia graminis Pers.). — Though in 

 earlier years this rust was thought to grow indiscriminately 

 upon a great variety of grasses, recent, thorough study has 

 shown that what was formerly regarded as one species is in 

 reality a number of races or varieties grouped under one 

 name. Collected on about 70 species of wild and cultivated 

 grasses including wheat, oats, rye, and barley, this rust is 

 now separated into eight or more biologic forms. See p. 277. 



It is the most serious of the rusts, of practically world- 

 wide distribution, and causes more damage in the Central 

 States than any other rust except the oat black-stem-rust. 

 It is injurious to oats, rye, and barley as well as wheat. The 

 damage done fluctuates largely. The injury is greater to 

 spring wheat than winter wheat. In 1916, the direct loss 

 was placed at $110,000,000, in four states, 200,000,000 

 bushels in the United States, and 100,000,000 more in 

 Canada. Total loss of the crop often results in Kentucky, 

 Indiana, Texas, Michigan, and Ohio. 



In the spring or cluster-cup stage upon the barberry, 

 swollen spots are produced upon the leaves, fruit, or young 

 stems. These spots upon one side bear the cups in abundance 

 and upon the other side appear as pale, circular regions which 

 bear the small, black pycnia. 



Upon the wheat the rust shows first its uredinia, which 

 come later than the uredinia of the orange-leaf-rust, and 

 are of more brownish tinge. The sori are most common 



