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MANUAL OF BOTANY 



trated by an incompletely septate mycelium. Dm-ing the 

 summer this mycelium produces patches of gonidia, each borne 

 upon a short stalk. These develop underneath the epidermis 

 of the host, and, being of a yellow or reddish colour, give the part 

 a rusty appearance. These are known as uredospores or 

 uredogonidia. These escape by rupture of the epidermis {fig. 

 849, a), and are blown upon other grass plants, where they ger- 

 minate, and the hypha penetrates the host through a stoma. In 

 the interior a mycehum is produced, which again produces 

 patches of uredospores. 



Towards the end of the summer the same mycehum gives 



Fig. 849. 



Fig. 850. 



Fig. 849. A. Grass leaf infested with Fuccinia graminis^ showing the uredo- 

 spores bursting through the epidermis of tiie leaf. E. Teleutospore ger- 

 minating and producing promycelium with sporidia. Fig. 850. Teleuto- 



spores of Fuccinia graminis bursting through epidermis of straw. After 

 Kny. 



origin to black patches which are visible upon the straw. These 

 are composed of numbers of compound gonidia, two together 

 upon a single stalk, developed as before by abstriction {fig. 850). 

 These, which are called teleutospores, or teleutogonidia, have 

 thick black walls and are very resistant. They remain quiescent 

 tin the spring, when one or both of the cells germinates, produ- 

 cing a small promycehum, usually of four cells. Each cell puts 

 out a small gonidiophore, from which a small gonidium, called a 

 sporidium, is developed by abstriction {fig. 849, b). From a re- 

 semblance to the cells which abstrict the spores in the next group, 

 these cells are sometimes called proto-hasidia. The sporidium 

 is a very small thin-waUed structure, and from its lightness it is 



