190 



MORPHOLOG Y. 



is formed of similar rows of cells, which, instead of separating 

 into gonidia, remain united to form a wall. These cups are 

 usually borne on the under side of the leaf. 



405. Spermagonia. Upon the upper side of the leaves in the same spot 

 occur small, orange-colored pustules which are flask-shaped. They bear 

 inside, minute, rod-like bodies on the ends of slender threads, which ooze 



Fig. 317. 

 Section of an aecidium (cluster cup) from barberry leaf. (After Marshall-Ward.) 



out on the surface of the leaf. These flask-shaped pustules are called 

 spermagonia, and the minute bodies within them sfermatia, since they were 

 once supposed to be the male element of the fungus. Their function is not 

 known. They appear in the spots at an earlier time than the cluster cups. 

 406. How the cluster-cap stage was found to be a part of the wheat rust. 

 The cluster-cup stage of the wheat rust was once supposed also to be a dif- 

 ferent plant, and the genus was called ezcidium. The occurrence of wheat 

 rust in great abundance on the leeward side of affected barberry bushes in 

 England suggested to the farmers that wheat rust was caused by barberry 

 rust. It was later found that the aecidiospores of the barberry, when sown 

 on wheat, germinate and the thread of mycelium enters the tissues of the 

 wheat, forming mycelhim between the cells. This mycelium then bears 

 the uredospores, and later the teleutospores. 



