306 



THE BASIDIOMYCETES 



prepared and are invaluable in the solution of taxonomic prob- 

 lems. In Zundel's account 1 species of Cinctractia, 28 of Soro- 

 sporium, 39 of Sphacelotheca, 3 of Tolyposporella, and 5 of Usti- 

 lago are treated. 



Fig. 118. A. Chlamydospore of Urocystis occulta. B. Tip of hypha (ba- 

 sidium) surmounted by a fascicle of sterigmata bearing sporidia. C and D. 

 Copulation of sprout cells of Ustilago violacea, as a result of which the 

 cells are binucleate. (After Harper.) E, F, and G. Stages in chlamydo- 

 spore formation in Entyloma nyinphaeae. The binucleate cells enlarge, 

 the nuclei fuse, the walls of contiguous cells separate, and the chlamydo- 

 spores become thick-walled. (After Lutman.) H. Germination of fertile 

 cell from spore ball of Doassansia viartianoffiana, with ampuUiform sterig- 

 mata bearing elongate sporidia. /. Spore ball of D. martiano-ffiana, in sec- 

 tion, showing sterile periphery and sterile medullary region. (After Setchell 

 and Lutman.) /, K, L, M, N, and O. Successive stages in formation of 

 chlamydospores in Ustilago zeae. Uninucleate hyphal cells fuse, giving 

 rise to binucleate condition, whereupon the nuclei fuse and the cell walls 



thicken. (After Rawitscher.) 



Generic separations are based largely upon (a) the arrange- 

 ment of spores, whether occurring singly, in pairs, or in balls; 



(b) the nature of the smut sori, whether dustv or agglutinated; 



(c) the presence or absence of sterile tissue in spore balls; and 



(d) the color of the spores. 



