1898 | RESEARCH INTO GRAIN RUST 33 
even if they lie in water for four or five days. Such is the case for 
instance with the uredospores of yellow rust (Uredo glumarum), 
with zcidiospores of black rust (cidium Berberidis), and so on. 
The cause of this remarkable state of things has been a mat- 
ter of much perplexity, and many experiments were set on foot 
in order to learn a way of increasing the germinating power, at 
least to some extent. Such a way was finally discovered, which 
was to cool them. Ever since the old Roman days cultivators 
have observed that alternating cool nights and warm days favor 
the development of rust.. From this the thought came to me to 
cool the spores by putting them on ice, or by chilling them in 
water for several hours. How strange it is, indeed, that these 
experiments should often give positive results! The dormant 
power of germination is brought to life, and with certain kinds 
of spores only in this manner has it been possible to carry out 
infection experiments. This capricious germination partly 
accounts for the small propagation of the disease already men- 
tioned. But this alone does not give complete explanation, for 
such a restricted propagation is also to be observed in forms 
whose spores as a rule germinate very well. The whole cause 
must, therefore, be sought elsewhere. 
4. The spread of rust depends to an important degree upon the 
distances. 
For the purpose of explaining the outbreak and spread of rust 
in grain fields we have not generally been concerned with the dis- 
tances separating the fields from a suggested source of infection. 
The pustules of rust once appearing on the barberry, the primary 
source of the whole neighborhood’s infection was thought to have 
been found. It was believed that at first the nearest fields became 
rusted, through them in eight days afterwards the somewhat 
remote region, and so on. The farther from the original source, 
the more secure one could be. Sometimes, however, this pro- 
tective distance must apparently be considerable. Black rust has 
been observed in the Indian wheat fields with no barberry as the 
“Source of infection nearer than 300 miles, on the Himalayas. 
However, we sometimes find recorded a different opinion. Thus, 
