

RHAMNUS IN THE DISSEMINATION OF CROWN RUST. 5 



uredospores are dry and may be deposited and carried on a number 

 of times before they are deposited finally and find favorable condi- 

 tions for germination. 



co/w 



CO/?A/ 



Fig. 2.— Sketch map of about 5 square miles surrounding the hedge of buckthorn (Rhamnus cathartica) 

 near Hinton, Iowa, showing the location of oat fields and the percentage of uredospore infection caused 

 by the spread of secidiospores from the hedge from May 22 to 29, 1921. (Compare with fig. 4.) 

 ) 



FACTORS INFLUENCING THE SPREAD OF .ECIDIOSPORES. 



The degree of infection was influenced to some extent by the 

 topography of the ground. In the oat field entirely surrounded by 

 the hedge the grain in the ravines was more heavily infected than 

 that on higher levels. The dew formed first in the ravines and 

 remained there longer in the morning, which may partly explain the 

 increased percentage of infection found there. 



