88 



MANUAL OF BOTANY 



trated by an incompletely septate mycelium. During 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 uredosi^ores 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 mycelium is i)rpduced, which again produces 

 •patches of uredospores. 



Towards the end of the summer the same mycelium gives 



Fig. 849. 



Fig. 850. 



Fig. 849. A. Grass leaf infested ■with Puccinia graminis, showing the uredo- 

 spores bursting through the epiderrois of the leaf. B. Teleutospore ger- 



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



spores oi 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 resistent. They remain quiescent 

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

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

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

 sporidiu7n, 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 jiroto-hasidia. The sporidium 

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



