400 



THALLOPHYTES 



thought that the basidiospores started the disease directly on the 

 Grass host, but experiments have shown that they will not grow 

 on this host. Experiments have also shown that urediniospores 

 are ordinarily killed by freezing weather and therefore are rarely 

 able to live over winter where the temperature goes much below 

 freezing. It has been suggested that some hyphae may enter the 

 kernels of the diseased plants and remain dormant until the seed 

 is planted and then infect the seedling, but this theory is not 

 generally accepted. Another suggestion is that the wind carries 

 the urediniospores northward from the Southern states where they 



rrtrffV"'"'' 



Fig. 358. — Apple affected with Cedar Rust. From Technical Bulletin 9, 

 Virginia Agr. Ejcp. Sta. 



are able to live over winter. It is also probable that the aecio- 

 spores may be carried a considerable distance by the wind and 

 thus reach grain fields not in the immediate vicinity of Barberry 

 bushes. Then there is the probability that the disease may start 

 on the wild Grasses growing near the Barberry bushes, and be 

 passed along by the urediniospores from one patch of Grass to an- 

 other until grain fields far away are reached. 



No satisfactory preventative for the Black Rust has been dis- 

 covered. We are not able to control the spores. It is generally 

 believed that the eradication of all of the Common Barberry 

 bushes would do much toward ehminating this Rust. The most 



