-' 



FIG. 41. Cronartium ribicolum, a fungus showing alter- 

 nation of generations, i, uredospore and teleutospore stages 

 on leaf of black currant ; 2, uredospores, a, and teleutospores, 

 b, grown together to form an erect, hair-like structure ; 3, 

 uredospore; 4, four teleutospores, two of which are germinat- 

 ing : one of the germ-tubes bears four promycelial or secondary 

 spores ; 5, aecidial form of fruit on living bark of Weymouth 

 pine ; 6, aecidiospores. Figs, i and 5, nat. size ; the remainder 

 mag. 



