CLASSIFICATION 30$ 



somes undergo reduction at the same division of the nucleus, 2 

 of the promyceHal cells will contain nuclei of 1 sexual phase and 

 the other 2 of the opposite phase. If, on the other hand, 1 

 chromosome pair undergoes disjunction at the first nuclear divi- 

 sion and the other at the second, then the resultant 4 promycelial 

 nuclei possess 4 different combinations of the sexual factors. 



Among Tilletiaceae also the dicaryotic condition arises vari- 

 ously. In Tilletia tritici Rawitscher (1922) found that 8 to 16 

 nuclei are developed within the short 1 -celled promycelium. x\t 

 the apex of the promycelium a number of filamentous cells are 

 produced, each of which contains a single nucleus. While they 

 are still attached or after they have been dislodged, tubes are 

 formed, connecting them in pairs. Plasmogamy follows, and 

 slender mycelia form, each cell of which is binucleate. These 

 mycelia delimit binucleate, falcate sporidia until the available nu- 

 trient is exhausted. These sporidia in turn can produce infection 

 of the appropriate host, and eventually chlamydospores are devel- 

 oped. 



In Doassmisia sagittariae the cells formed on the promycelium 

 do not conjugate in pairs [Rawitscher (1922)]. They fall away 

 and germinate to form uninucleate mycelia, and the dicaryons 

 arise from hyphal fusions within the host tissues. 



Classification. The smuts, as has been stated, include the two 

 famiUes Ustila^inaceae and Tilletiaceae. Most mycologists also 

 include a third family, the Graphiolaceae, typified by Graphiola 

 phoemcis, occurring on the foHage of date palm, Fhoenix dac- 

 tylifera, and of other palms. The structure and classification of 

 this species w^ere made possible by the work of Killian (1924), 

 who established that its spores arise as chlamydospores and that 

 the nuclear activities during spore formation and germination are 

 like those of Ustilaginales. Stylina and Shropshiria are also in- 

 cluded among the Graphiolaceae. 



In the monograph by Clinton (1906) the Ustilaginaceae in- 

 clude 11 genera, and the Tilletiaceae 8 genera. From the work 

 of others the Ustilaginaceae now have 12 genera, and the Tille- 

 tiaceae 13. Various monographic studies for different areas, such 

 as that of Ale Alpine (1910) of the smuts of Australia, that of 

 Setchell (1892) on species of Doassansia, or that of Zundel (1930) 

 of the smuts on Andropogon in all parts of the world, have been 



