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 uredospores 
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 uredospores northward from the Southern states where they 
1 
Fic. 358. — Apple affected with Cedar Rust. From Technical Bulletin 9, 
Virginia Agr. Exp. Sta. 
are able to live over winter. It is also probable that the aecidio- 
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 uredospores 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 tocontrol the spores. It is generally 
believed that the eradication of all of the Common Barberry 
bushes would do much toward eliminating this Rust. The most 
