402 



HOT A X Y 



U. Hordei, and I'. Tritici sf yet urn, which were formerly united as U. Carbo, cause 

 the "smut" or "brand" of Oats, Barley, and Wheat. The mycelium penetrate> 

 the ovary, and forms dark brown, dust -like masses of escaping resting -spores. 

 U. Afaydis produces on the stalks, leaves, and inflorescences of the Maize tumour- 

 like swellings filled with brand-spores in the form of a black powder. Other >peei.-s 

 live on the leaves of different grasses ; while U. violacea ( = U. antherarum) occurs 

 in the anthers of various Carophyllaceae (e.<j. /,//<///., Saponaria), and fills the 

 pollen-sacs with brand-spores. 



The brand-spores of Ustilago fall to the ground, and after a period of rest give 

 rise, on germinating, to a short tube (promycelium) which becomes septatcd \>\ 



three or four transverse walls (Fig. 346 ), and, 

 functioning as a basidium, produces ovate basidio- 

 spores or conidia (sporidia), both laterally from the 

 upper ends of the intermediate cells, and also from 

 the tip of the terminal cell. When abundantly 

 supplied with nourishment, as when cultivated in 

 a nutrient solution, conidia are continuously ab- 

 stricted in large numbers (Fig. 345 (7), and then 

 multiply further by budding, cell-fusions or union 

 of nuclei frequently occurring as a preliminary (C, 

 D}. After the food-supply of the substratum is 

 exhausted, the conidia grow out into mycelial hyphse. 

 The formation of the conidia in the damp manured 

 soil of the grain fields is accomplished during a 

 saprophytic mode of existence, but the hyphal fila- 

 ments which are eventually produced become para- 

 FIG. 34i ; . i'xtilugo Scabosine. A, sitic > an d penetrate the young seedlings as far as the 

 yoiiiij; hasidiuni with four nuclei apical cone where the inflorescence takes its origin, 

 formed on germination of the T ue mycelium continues its development in the 

 inflorescence) an d ultimately terminates its exist- 

 ence by the production of brand-spores. No conidia 

 are formed on the host plant itself. 

 In addition to the infection of young plants either resting-spores or the conidia 

 resulting from their germination may be carried to the stigmas of the grass- flowers (~ 4 ) 

 and germinating there produce a mycelium which penetrates to the young seed> 

 and passes the winter in the embryo-plants. Such infection of the flowers may 

 alone take place as in Ustilago Tritici, U. Hordei, and U. antherarum, or the seed- 

 ling may more often be infected as in U. Avenae, U. Sorghi, U. Panici miliacei, 

 U. Crameri. The Smut of Maize can infect all parts of the plant while in a young 

 state and the disease is limited to the infected spots. 



The life-history of the Tilletiaceae is similar to that of the Ustilaginaceae. The 

 best-known species are Tilletia Tritici (=T. Caries] and Tilletia laevis, the fungi 

 of the stink-brand of wheat. The resting-spores till the apparently healthy grains 

 and smell like decayed fish. In the first- named species the resting-spores are 

 reticulately thickened ; those of T. lacvis, on the other hand, are smooth-walled. 

 Unlike the Ustilaginaceae, the germ-tube gives rise only at its apex to filiform 

 basidiospores, which are disposed in a whorl, and consist of four to twelve spores 

 (Fig. 347 A). The basidiospores also exhibit the peculiarity that they coalesce 

 with one another in pairs in an H-form. Such cell fusions also occur between 

 germinating conidia of the Ustilagineae, but are not accompanied by nuclear fusions. 

 The filiform spores germinate readily, and produce sickle-shaped conidia at the apex 



B 



resting spore ; S, spore-formation 

 (in the 4-ei'lh-il hasiilium. (After 

 HARPER.) 



