401 



basiclium in the Hymenomycetes and Gasteromycetes is unicellular, 

 and bears as a rule four spores at the summit ; these may be sessile 

 or situated on sterigmata (Figs. 343, 355). 



The Ustilagineae are of interest since in one family the basidia 

 are divided, and not always strictly four-celled, while in the other 

 the basidia are undivided. The number of spores produced is not a 

 definite one but often very large. 



In addition to conidiophores differentiated as basidia, the Basidio- 

 mycetes produce other forms of conidia as accessory fructifications in 

 many species. These appear in the Ustilagineae as the smut-spores, 

 and as the rust-spores in the Uredineae. In these groups the basidia 

 arise directly from spores of this kind (Figs. 344 A, 346). In other 

 Basidiomycetes, if a few simple forms are disregarded, the basidia are 

 always borne upon or within more or less complicated fructifications. 

 The layer in which the basidia are associated together is termed the 

 hymenium. 



Order 1. Ustilagineae (Smut-Fungi) ( 48 - 49 . 73 ) 



The Ustilagineae are parasites, and their mycelium is found ramifying in higher 

 plants, usually in definite organs, either in the leaves and stems, or in the fruit or 

 stamens. The Gramineae in 

 particular serve as host plants ; 

 certain species of Ustilagineae 

 are in a high degree injurious 

 to cereals, and produce in the 

 inflorescences of Oats, Barley, 

 Wheat, Millet, and Maize the 

 disease known as Smut. 



The mycelium ultimately 

 produces resting-spores by the 

 formation of additional trans- 

 verse walls, and by the divi- 

 sion of its profusely branched 

 hyphse into short swollen cells 

 (Fig. 345 A). The cells be- 

 comeroundedoffand converted 

 into spores, within a gelatinous 

 envelope, which, however, 

 eventually disappears. The 

 spores then become invested 

 with a new, thick, double 

 wall. In this way the mycel- 

 ium is transformed into a dark 

 brown or black mass of spores. 



These Smut-spores, brand-spores, or resting-spores are scattered by the wind, and 

 germinate only after an interval of rest, producing the basidia in the succeeding 

 spring ; the formation of these is characteristically different in the two families of 

 the Ustilaginaceae and the Tilletiaceae. 



The most important genus of the Ustilaginaceae is Ustilago. Ust. Avenae, 



2 D 



FIG. 345. .!, Ustilago olivacea. Mycelial hypha in process of 

 forming smut-spores ( x 400). B-D, Ustilago segetum: B, 

 germinating smut-sport- (i-l), cultivated in nutrient solu- 

 tion ; t, transversely septate, liasidiuin with lateral and 

 terminal basidiospores (conidia) (e) ( x 450); C, germinating 

 smut -spore lying in the nutrient solution surrounded 

 by ab.stricted conidia, which are multiplying by budding 

 ( X 200) ; I), an aggregation of budding conidia ( x 350). 

 (After BREFELD, from v. TAVEL, Pilze.) 



