RASPBERRY RUST 



259 



upper surface of the leaves, less frequently forming elongated 

 patches on the leaf stalks or stems. Next follows the 

 uredo stage, which differs but little from the aecidium as 

 seen with the naked eye : the pustules are small, pale orange, 



Fig. 66. Phragmidium rubi-idaei. i, under surface cf a 

 raspberry leaflet showing pustules of teleutospores ; 2, teleuto- 

 spore, x 350 ; 3, section through an aecidium ; a, chains of 

 warted spores ; b, b, large club-shaped sterile cells forming 

 the covering of the aecidium, x 300 ; 4, uredospores, x 300. 



and scattered, not arranged in circles. Later in the season, 

 the numerous small black clusters of teleutospores are 

 produced on the under surface of the leaves. 



The teleutospores are very beautiful objects seen under 

 the microscope, each spore consisting of a single row of 



