RUSTS 



281 



the work of reproduction in spring, whence they are called 

 " winter spores," in contradistinction to the uredos or 

 "summer spores," whose activity seems to be confined to 

 the warm months. 



<^-^1i^~lilhY\'&'^ffM Wt 



539. — Uredospores of wheat rust, Puccinia graminis, magnified (from 

 Coulter's " Plant Structures "). 



Under the microscope the teleutospores appear as long, 

 two-celled bodies with very thick black walls (Fig. 540). 

 Since they are developed from the same mycelium with the 



540. — Teleutospores of wheM rust, magnified (from COULTER'S 

 " Plant Structures "). 



uredospores, and are not a product of the latter, but collat- 

 eral with them, the two constitute a single generation, and 

 belong to one and the same stage in the life history of the 

 plant. 



402. Sporidia. — In spring the teleutospores begin to 

 germinate, each cell producing a small filament, from 

 which arise in turn several small branches. Upon the tip 



