306 



Diseases of Economic Plants 



periments it has been impossi- 

 ble to infect one of these hosts 

 from the other. It is invari- 

 ably present where rye is 

 grown and is particularly 

 abundant in the Southern 

 States, though notwithstand- 

 ing its universal presence it is 

 not destructive. The uredi- 

 nial mycelium remains alive 

 in the South and continues to 

 produce spores during winter 

 in the leaf, as it probably 

 does in colder climates as well. 

 It is possible that it is in this 

 way carried from season to 

 season by volunteer rye in 

 the fields. The cluster-cup 

 stage occurs upon a member 

 of the Borage family, but has 

 never been found occurring 

 naturally in America. 



Stem-smut ^-^' '"^"^ {Urocystis 

 occulta (Wallr.) Rab.). — Un- 

 like many of the cereal smuts 

 the stems and leaves as well 

 as the floral parts are affected. 

 It may be recognized by the 

 usual, dusty, black spores, 

 which occur especially at the 

 joints. While this disease 

 does not directly attack the 

 grain, it does diminish the 

 yield by weakening the plant. 

 Loss from 25 to 40 per cent is 

 reported in Minnesota, 60 per 

 cent in Australia. Seedlings may be infected from spores 



Fig. 162. — Head of rye attacked 

 by anthracnose. After Manns. 



