300 THE BASIDIOMYCETES 



believed to arise by spontaneous generation. The work of 

 Prevost appears to constitute the first adequate experimental dem- 

 onstration that fungi may cause disease of plants. He described 

 the bunt fungrus as an internal parasitic plant and traced its de- 

 velopmental cycle from the "globules" or "seeds" lodged on the 

 strains to their reappearance within the inflorescence. His field 

 trials with appropriate controls also demonstrated that the disease 

 may be successfully treated by steeping seed wheat in a solution 

 of copper sulphate. Evidently smut diseases had earlier been 

 controlled, but only by empirical procedures. The Moors and 

 Fellahs had long practiced casting seed grain through fire, pre- 

 sumably because fire was regarded, from religious rites, as a 

 means of purification. In 1660 the efficacy of brining in disin- 

 fecting^ seed wheat had also been discovered accidentally. 



Types of host involvement. Smuts may attack any part of 

 the plant above ground, but involvement is generally limited to 

 one ororan. In Cinctractia cartels and Tiibiircima trientalis the 

 perennial mycelium may occupy both shoots and rhizomes. 



In Ustilago zeae sori may form on all parts of the plant. They 

 are commonly present on ears, tassels, leaves, and stalks and may 

 also appear on the roots. In U. avenae, U. levis, U. hordei, and 

 Tilletia tritici the mycelium occurs in the stem apex and advances 

 into inflorescences as they form. 



The mycelium usually causes little, if any, distortion of the 

 host. Oats and wheat attacked by Ustilago avenae and U. tritici, 

 respectively, may be somewhat dwarfed. Ustilago zeae on corn 

 may cause considerable hypertrophy. Ustilago treubii, on stems 

 of Folygommi chinense in Java, stimulates the formation of elab- 

 orate oralis that resemble fructifications of Cantharellus. In east- 

 ern Asia U. esciilenta deforms the shoots of Zizania latifolia, and 

 natives eat the deformed stems as a salad [Hori (1907)]. Ustilago 

 z'iolacea induces the staminal rudiments of carpellate flowers of 

 Lychnis dioica to develop apparently normal stamens, but on de- 

 hiscence pollen is found to have been replaced by smut spores. 



Spores and their development. The structure which charac- 

 terizes all smuts is the smut spore, or chlamydospore, with a 

 thickened wall that is smooth or variously sculptured and usually 

 brown, black, or violet in color. Lutman (1910) studied spore 

 formation in a number of orenera. He and all others who have 

 devoted their attention to the origin of smut spores agree that 



