452 



BOTANY 



In addition to basidia, the Basidiomycetes, like the Ascomycetes, produce 

 various forms of conidia as accessory fructifications in many species. The origin 

 of asexual spores by hyphal cells rounding off and developing a thick wall 

 and their ultimate separation is different from that of conidia (chlamydospores 



FIG. 397.Armillariamellea. A, Young 

 basidium with the two primary 

 nuclei ; B, after fusion of the two 

 nuclei. Hypholoma appendiculatum, 

 C, a basidium before the four nuclei 

 derived from the secondary nucleus 

 of the basidium have passed into the 

 four basidiospores. D, Passage of a 

 nucleus through the sterigma into 

 thebasidiospore. (After RUHLAND.) 



FIG. 398. Basidium of one of the 

 Tremellineae (Tremella lutescens) (after 

 BREFELD). (x 450. From v. TAVEL, 

 Pitee.) 



according to BREFELD). These appear in the Ustilagineae as the smut-spores, 

 and as the rust -spores in the Uredineae. In the former the basidia arise 

 directly from spores of this kind (Fig. 400), in the latter from a definite type 

 of rust-spore (Fig. 403, 2). In other Basidiomycetes, if a few simple forms are 

 disregarded, the basidia are always borne upon or within more or less com- 

 plicated fructifications. The layer in which the basidia are associated together 

 is termed the hymenium. These fructifications correspond to those of the 

 Ascomycetes, but no sexual organs are concerned in their origin. The young 

 basidia, corresponding to the smut- and rust-spores, here arise from hyphae of 

 the fructification without the formation of chlamydospores. 



Order 1. Ustilagineae (Smut Fungi) ( 76 ) 



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 

 transverse walls, and by the division of its profusely -branched hyphae into 

 short swollen cells. The cells become rounded off and converted into spores 

 within a gelatinous envelope, which, however, eventually disappears. The spores 

 then become invested with a new, thick, wall. In this way the mycelium is 



