SECT. I 



CRYPTOGAMS 



103 



Ustilagineae are in a high degree injurious to cereals, and produce in the inflor- 

 escences 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 (Fig. 335, A). 

 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 transformed into 

 a dark brown or black mass 

 of spores. These smut-spores, 

 brand-spores, or resting-spores 

 are scattered by the wind, 



Fk;. 335. — .(, U^tllago ulivacca. Mycelial liyplia in luocess of 

 forming; siiiut-sporps (x 400). B-D, Ustilwic i^cgctmn : B, 

 germinating smut-spore (cZ), cultivated in nutrient solu- 

 tion ; t, trans\ersely septate basidium with lateral and 

 terminal Ijasidiospores (conidia) (<■) ( x 450) ; C, germinating 

 smut-.spore lying in tlie nutrient solution surrounded 

 by abstricted conidia, winch are multiplying by budding 

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

 (After Brefei.d, from v. Tavel, Pil-c.) 



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. J'st. Avenac, 



IL Rordci, and U. Tritici scrjetum, which were 

 formerly united as U. Carbo, cause the "smut" or 

 "brand" of Oats, Barley, and Wheat. The mycelium 

 penetrates the ovary, and forms dark brown, dust- 

 like masses of escaping resting-spores. U. Maydis 

 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 species 

 live on the leaves of different grasses ; while V. 

 violacea (= U. antheranom) occurs in the anthers of 

 various Carophjdlaceae {e.g. Lychnis, 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 ([>romycelium) which becomes 



divided by three or four transverse walls (Fig. 



336, £), and, functioning as a ba.sidium, produces 



young basidium with four nuclei ovate basidio - s])ores or conidia (sporidia), both 



formed on germination of the laterally from the up]>er ends of the intermediate 



resting spore ;i5, spore-formation egUg^ ^nd also from the tip of the terminal cell. 



When abundantly supplied with nourishnrent, as 

 when cultivated iu a nutrient solution, conidia 



are continuously abstricted in laige numbers (Fig. 335, C), and then inultiph' 



2d 1 



on the 4-celled basidium. 

 Harper.) 



(After 



