IQO 



MORPHOLOGY. 



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 



Section of an afcidiuni (cluster cup) from barberry leaf. (After Marsliall-W'ard.l 



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

 spermagonia^ and the minute bodies within them spcrniatia^ since the\' were 

 once suppose<l to bt; the male elemc-nt nf the fungub. Their tunction is not 

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



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

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

 ferent plant, and tlie genus was called tCiidiiini. The occurrence ol wheat 

 rust in great abundance on the leeward siile of affected barberr>' bushes in 

 Kngland suggested to the farmers that wheat rust was caused bv liarherrv 

 rust. It was later found that the oecidiosporcs of the IxirlK'rry, when sown 

 on wheat, germinate and (he thread of mycelium ei.lers the tissues of the 

 wheat, forming mycelhim l^etween the cells. This mycelium tiien bears 

 the uredospores, and later the teleutospores. 



