UREDINALES 



579 



In another direction, Uromycladium and Ravenelia have been dif- 

 ferentiated. In the simpler forms, as Uromycladium simplex (McAlpine, 

 1905), there arises at each terminal cell a teliospore deceptively similar 

 in form and structure to Uromyces (Fig. 389, 9). The basal cell changes 

 into a double-walled, hyaline cyst c filled with a gel capable of swelling (a 

 characteristic of both genera). Exceptionally, the cysts may be absent 

 and replaced by a second teliospore. In other forms, e.g., U. bisporum, 



Fig. 392. — Ravenelia cassiaecola. A. Infected twig of Cassia nictitans, with telium on 

 stem and uredinium on leaf. B. Enlarged section of stem. C. Section through periphery 

 of telium on stem. The cuticle is ruptured. Mycelium visible in the cells of the bark. 

 Telium shows mature and young heads, one in cross section. Ravenelia appendiculata. 

 D. Head seen from above. E. Isolated spore. (A, natural size; B X 10; C X 350; 

 D, E X 400; after Dietel, 1906.) 



the sporiferous hyphae regularly produce two teliospores without cysts. 

 Still others, as U. maritimum, develop two teliospores (Fig. 389, 6 and 7) 

 above a third cell from which a cyst is developed; here also, in an excep- 

 tional case, the cyst may be replaced by a third teliospore. And finally 

 in the highest forms, e.g., U. Tepperianum, three teliospores without cysts 

 are regularly formed on the stipe cells. 



In Ravenelia (Fig. 392), a very significant development of spore heads 

 appears (Parker, 1887; Dietel, 1906). The first fundament of the heads 



