314 GENERAL MORPHOLOGY OF PLANTS 



propagative stage, because by means of successive crops of nu- 

 merous spores in one season the fungus is widely propagated. 



464. The black rust of wheat (teleuto stage). The myce- 

 lium in the wheat formed by the germinating aecidiospores from 

 the barberry, as well as that formed by the germinating uredo- 

 spores, often produces another kind of spore, the teleutospore. 

 These teleutospores are sometimes formed in a separate sorus 



(a teleutosoms), or sometimes they are mixed with the uredo- 

 spores. In the wheat rust the teleutospores are two-celled, 

 with thick brown walls, and the stalk usually remains attached 



( fi g- 273)- 



465. Germination of the teleutospores and infection of 

 the barberry. The teleutospores of the wheat rust rest during 



Fig. 274- Fig. 275- Fig. 276. 



Teleutospore germinating, Promycelium of germinat- Germinating sporidia en- 



forming promycelium. ing teleutospore, forming tering leaf of barberry by 



sporidia. mycelium. 



Figs. 274-276. Puccinia graminis (wheat rust). (After Marshall-Ward.) 



the winter on leaves and stems lying on the ground. In the 

 spring each cell germinates, putting forth a tube through a germ 

 pore near the apex of each cell (figs. 274, 275). This tube* 



* Promycelium, 



