CHAPTER XXXIV 

 USTILAGINALES 



The Ustilaginales, or smuts, include several hundred species which 

 parasitize higher plants, develop their thick-walled spores (smut spores) 

 in definite organs and impart to these organs a burnt or charred appear- 

 ance. In contrast to the Uredinales, they are saprophytic in a portion 

 of the life cycle, and some of them may complete the whole cycle in 

 artificial culture. 



Their mycelium consists of slender, hyaline hyphae whose cells, 

 corresponding to the cytological life cycle, in some species are uni-, in 

 others binucleate; occasionally, as in the higher Basidiomycetes, they can 

 become multinucleate (Fig. 397, 1). In some forms, as in the corn smut 

 Ustilago Zeae (U. Maydis) and in Entyloma and Doassansia, they grow 

 only in the region of initial infection (i.e., in all the growing parts of the 

 plants, even the roots) where they form their smut sori. In most 

 other forms they penetrate the whole plant or single sprouts 

 and much later form sori in leaves or fruits. Ustilago Tritici, the flag 

 smut of wheat, and U. nuda, the flag smut of barley, infect flowers; the 

 mycelium winters in the seeds, grows behind the growing point the 

 following year and, at the end of the growing season, it forms a sorus in 

 the ear. In most other cereal smuts, as Tilletia Tritici, bunt of wheat, 

 U. Avenae, the flag smut of oats, U. levis, the covered smut of oats, U. 

 Hordei, the covered smut of barley, U. Crameri, the millet smut, and 

 Tuburcinia occulta (Urocystis occulta), the stem smut of rye, the infection 

 takes place in spring in the young seedlings, the mycelium grows up the 

 stem behind the growing point and forms the sorus : in T. Tritici and U. 

 Crameri in the ovary; in U. Hordei in the ears; in U. Avenae and U. levis 

 in the panicle; in Tuburcinia occulta mainly in the stem and leaves. In 

 Cintractia Caricis and Tuburcinia Trientalis the mycelium is perennial in 

 the rhizome and the shoots. In the former, it forms the sorus in the 

 ovary, in the latter in the stems and leaves. 



The hyphae are mostly intercellular; in some species, as in the Uredin- 

 ales, for the sake of nourishment they penetrate the host cells with 

 capitate or racemoid haustoria and thereby cause direct injury to the 

 plant. Thus the specimens of Trientalis infected by Tuburcinia are 

 recognizable by the pathological thickening of their stems and the smaller 

 size and lighter color of their leaves. In Entyloma Nymphaeae the haus- 

 toria arise as special branches of the intercellular hyphae and swell 



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