Adams: Infection of Crataegus by Gymnosporangium 47 



plums. Figure 2 shows the upper growth of a hawthorn in the 

 early spring with the numerous hypertrofied branches as the 

 result of previous infection. On the larger branches the hyper- 

 trofies indicate perennial character of the rust infection. The 

 aecia on the branches always preceed the appearance of the aecia 



Fig. 3. A branch showing the hypertrofied development of the young 

 growth, modified branches and germinal buds as the result of infection by 

 G. germinale. 



on the fruit of the hawthorns. Infection with G. germinale on 

 the fruit of the hawthorns is most conspicuous and the fruits are 

 usually completely covered with the cylindrical aecia. 



Infection with G. globosum, which occurs on the leaves of the 

 hawthorns, has been observed to cause partial defoliation: The 

 aecia are also commonly found developing on the calyx lobes of 



