GRASS-RUST. 



417 



astrous effects on them as on wheat. The red rust or uredo 

 state appears from early spring until fall. It consists of micro- 

 scopic one-celled rough spores, borne on branches of a myceli- 



FIG. 161. Grass-rust. A, germinating teleutospore, t; B, promycelium, with sporl- 

 dia: C, s p, sporidium, germinating on the lower side of a leaf; M, a germinating 

 uredospore. (From DeBarry.) 



um that vegetates within the grass, and only appears on the sur- 

 face to fruit, which propagate the disease rapidly in damp warm 

 weather. Toward the end of the season the same mycelium 

 bears a second form of fruit two-celled teleutospores or winter- 

 spores that form dense elongated black cushions where they 

 break through the epidermis, often covering the greater part of 



