418 



CLASS BASIDIOMYCETEAE 



cent of the North American species occur in members of the grass family 

 (Poaceae) and about 14 per cent on sedges (Cyperaceae) with about 19 

 per cent in Dicotyledons, particularly in the Polygonaceae and the Aster- 

 aceae. In the majority of species the spores are produced in the ovaries or 

 other parts of the flower, or the whole inflorescence may be involved. Some 

 species produce their sori in the leaves or stems of their hosts. 



The largest genus is Ustilago with over 300 species. Its spores are pro- 

 duced singly in a powdery mass. Many serious enemies of cultivated 

 plants are found in this genus, e.g., U. avenae (Pers.) Jens, and U. levis 

 (Kellerm. & Swingle) Magn., destroying the spikelets and inflorescence of 

 oats {Avena saliva L.), U. zeae (Beckm.) Unger, producing smut galls on 

 maize {Zea mays L.), U. hordei (Pers.) Keflerm. & Swingle and U. nuda 

 (Jens.) Kellerm. & Swingle on barley {Hordeum sativum L.), U. tritici 

 (Pers.) Rostr. on wheat {Triticum spp.), U. striiformis (West.) Niessl on 

 Poa pratensisL., U. violacea (Pers.) Fuckel on Dianthaceae, etc. Sphacelo- 

 theca differs from Ustilago in having the powdery mass of teliospores sur- 

 rounded by a pseudoparenchymatous layer of fungus tissue. S. sorghi 

 (Link) Clinton is injurious to the ovaries of Sorghum vulgare Pers. and 

 related species. In Schizonella the teliospores are in twos, otherwise much 

 as in Ustilago. S. melanogramma (DC.) Schroet. produces long black sori 



Fig. 141. Subclass Teliosporeae, Order Ustilaginales, Family Ustilaginaceae. (A) 

 Spore ball of Sorosporium saponariae Rud. (B) Spore Imll of Tohjposporium junci 

 (Schroet.) Woron., some of the spores germinating to form promycelia. (C) Ustilago 

 kuehneana Wolff, teliosporo germinating with whorls of sporidia at the septa of the 

 promycelium. (D) Schizonella melanogramma (DC.) Schroet. Tc^liospores joined in 

 twos. (A, after Dietel, in Engler und Prantl: Die Natiirlichen Pflanzenfamilien, 

 Zweite Auflage, vol. 6, pp. 1-98, Leipzig, W. Engelmann. B-C, after Brefeld: Unter- 

 suchimgen aus dem Gesammtgcbiete; der Mykologie, vol. 12, pp. 99-236. D, after 

 Clinton: Connecticut State Geological and Natural History Survey Bull, 6:1-44.) 



