38 BOTANICAL GAZETTE [JULY 
It may also be said here that from the writer’s observations he 
has concluded that heavy rainfall has little to do in any section of 
the country with producing infection by the rust, since there is evi- 
dence to show that by this means the spores are actually washed 
from the smooth surface of the plant to a great degree, rather than 
being afforded opportunity for germination and infection. A copious, 
misty dew, remaining until late in the forenoon on the thick asparagus 
= Sth 
SE 
Fic. 17.—Effect of rust at Milpitas, working from above downwards. Sep- 
tember 23, 1903. 
tops, appears to be the most important factor in producing infection. 
Experiments with uredospores, placed out of doors on dry glass 
slides night after night in various situations, support this view, as 
well as extended field observations. During rain the spores are 
washed from the slides and carried away. This would not occur 
so entirely upon the plant, but is true to a very large extent. During 
nights of very light dew no germination occurred. With slight dew, 
drying away early in the day, germination started, but the germ- 
tubes dried up before they would have had time for infection. Most 
