ORDER USTILAGINALES (tHE SMUTS) 



415 



Fig. 140. Subclass Teliosporeae, Order Ustilaginales, Family Ustilaginaceae, 

 Ustilago hordei (Pers.) Kellerm. & Swingle. Normal and abnormal germination of 

 teliospores. (A-G) Stages in the normal development. (H, I) Conjugation between 

 promycelial cells of opposite sexual phase. (After Htittig: Z. Botan., 24(6):529-577.) 



media. Both of these differ from the mode of growth of the dicaryon 

 mycehum produced when the two cultures are allowed to grow together. 

 Dickinson (1927, 1928) showed for Ustilago levis (Kellerm. & Swingle) 

 Magn., causing smut on oats, that infection does not take place unless 

 mycelia of two opposite sexual phases are present. Monocaryotic struc- 

 tures do not infect the host plants. It must be noted that Flerov (1923) 

 studied a strain of U. avenae (Pers.) Jens., also causing a smut on oats, in 

 which a monocaryon sporidium brought about infection by a monocaryon 

 mycelium which eventually produced uninucleate teliospores in which no 

 nuclear fusion occurred. From such teliospores arose a two-celled pro- 

 mycelium. Boss (1927) found the same to be true in Sphacelotheca ischaemi 

 (Fuckel) Clinton {Ustilago ischaemi). These are similar to the monocaryon 

 strain of Kunkelia nitens studied by Dodge (1924). (Fig. 140.) 



Hanna (1929b) demonstrated for U. zeae on maize that single sporidia 

 or conidia from cultures from single sporidia are able to infect the tender 

 meristem wdth a very slender germ tube composed of monocaryon cells. 

 This infection is usually of very limited extent and except in rare strains 

 no smut galls or teliospores are produced. When two sporidia of opposite 

 sexual phase infect the tissue in rather close proximity the slender mono- 

 caryon hyphae approach one another and unite and thenceforth develop 

 as a stout mycelium of dicaryon cells which penetrates the meristem in 

 all directions. These hyphae show numerous clamp connections. Eventu- 

 ally a smut gall is produced, filled with numerous teliospores. Similar 

 conditions exist according to this author in Sorosporium reilianum (Kiihn) 

 McAlpine, another species producing smut galls on maize. Christensen 

 and Stakman (1926) studied various mutations of corn smut. Christensen 

 (1929) reported three strains in which infection and production of large 

 galls occurred with monosporidial cultures. He did not follow the cyto- 



