ORDER USTILAGINALES (tHE SMUTS) 417 



by the production of promycelia and sporidia, and that the latter pair by 

 twos and then give rise to actively growing hyphae. On the contrary in 

 forma Poae-pratensis Davis it was shown by Leach and Ryan (1946) that 

 the teliospores germinate by the production of branched germ tubes of 

 indeterminate length. The earlier divisions of the teliospore nucleus are 

 regarded as meiotic so that this branching mycelium is considered to be 

 haploid. Here and there in this mycelium the nuclei begin to assort in 

 pairs and to undergo fusion. These hyphae wdth diploid nuclei grow and 

 the cells divide but soon the cells separate and form teliospores by thicken- 

 ing and becoming fusiform or limoniform with thickening and darkening 

 of the spore wall. These phenomena can be followed in artificial cultures 

 on agar. 



Another indication of the degeneration of this family is the fact that 

 in some species of Ustilago no promycelium is formed but from the telio- 

 spore there grow out cells that form short branching hyphae of yeast-like 

 cells. Bauch (1923) found that in Ustilago longissima and its variety 

 macrospora Davis the meiotic divisions of the diploid nucleus .of the ma- 

 ture teliospore take place in the teliospore itself and that then successively 

 sporidia are budded off from the latter. Into the first such sporidium two 

 nuclei enter while into those subsequently produced one nucleus may enter 

 or two, the latter being made possible by division of the nuclei remaining 

 in the teliospore. More often the two nuclei in the first sporidium are of 

 opposite sexual phase. In that case the sporidia become two-celled by the 

 formation of a septum and then these two cells unite through conjugation 

 tubes and grow out as slender dicaryon hyphae. The other sporidia if 

 uninucleate mostly remain one-celled but conjugate with sporidia of op- 

 posite sexual phase and then they too form the slender dicaryon "Such- 

 faden." Onl}^ under exceptional circumstances is a typical four-celled 

 promycelium formed, from the cells of which are budded off the sporidia. 

 The teliospores of the Ustilaginaceae vary in their longevity. Fischer 

 (1936) reports viable spores in herbarium specimens up to 3-10 years in 

 many cases and as high as 23 years for Ustilago hordei (Pers.) Kellerm. & 

 Swingle. 



Mutant forms have been observed frequently in smuts. Johnson et al. 

 (1940) report the occurrence of a mutant race of Sorosporium syntherismae 

 (Pk.) Farl., in which the teliospores are almost colorless but still retain 

 their ability to infect the host. 



When grown in liquid culture media with an abundance of soluble 

 carbohydrates the mycelium of smuts may break up into separate cells 

 resembling and multiplying like the asporogenous yeasts. Teliospores 

 sown in such media will frequently produce hyphae which become yeast- 

 like, instead of typical promycelia. 



The family includes over 450 species in about 12 genera. About 61 per 



