380 CLASS BASIDIOMYCETEAE 



separated the orders, placing the Ustilaginales in their Class Zygomycetes 

 while the Class Uredineae was placed between the two Classes Asco- 

 mycetes and Basidiomycetes, the affinities being considered to lie with 

 the former. Because of the fancied resemblance of the teliospores of some 

 Rusts to asci, Charles E. Bessey (1894) was inclined to include the 

 Uredinales and Ustilaginales in the Class Ascomyceteae, a position from 

 which he receded when the cytological phenomena of these groups became 

 better known. That they are rather closely related to the other Basidio- 

 myceteae the studies of Brefeld (1881 and later) and the cytological in- 

 vestigations of Sappin-Trouffy (1896), Harper (1898, 1902), and others 

 leave little doubt. That they stand apart from the majority of families of 

 that class is equally certain. The author beheves that the differences are 

 sufficiently great to warrant placing them in a separate subclass, a posi- 

 tion that does not deny their relationship within the Basidiomyceteae but 

 leaves each subclass much more homogeneous. 



The fungi of this subclass are parasitic. In the Order Ustilaginales 

 some of the species are capable of saprophytic growth in media rich in 

 food; in the Uredinales growth is strictly parasitic and the fungi have 

 never been cultured except on the living tissues of the host. The mycelium 

 is long, slender, and branching, growing intercellularly within the host. In 

 the majority of cases studied occasional or frequent haustoria are pro- 

 duced. The cells of the mycelium are mostly uninucleate in one stage of 

 development (monocaryon stage) and binucleate in the remainder of the 

 life cycle (dicaryon stage). As the cells of the latter type of mycelium 

 divide the two nuclei divide simultaneously so that one daughter nucleus 

 of each of the original nuclei is found in each of the two daughter cells. 

 This is the type of nuclear division to which the term "conjugate divi- 

 sion" was given. Clamp connections occur in many of the Ustilaginales 

 but have been rarely reported in the Uredinales. Finally, on the dicaryon 

 mycelium are produced certain larger cells, usually terminal to a hypha 

 or its branches, which become thicker walled. Within these cells the two 

 nuclei unite to form the only diploid nuclei in the life cycle of the fungus. 

 These cells are the teliospores. In the Ustilaginales (Smuts) these are often 

 spoken of as "chlamydospores," a misuse of this name which is rightly 

 applied only to vegetative cells which become filled with food and develop 

 thick walls to permit survival over winter or through other unfavorable 

 environments. In true chlamydospores there is no nuclear fusion and their 

 germination is in the manner usual for asexual spores. 



Plowright (1889) recognized tlfe essential homology of the teliospores 

 in the two orders. They have a typical manner of development. The 

 diploid nucleus divides by meiotic divisions into four nuclei, in the 

 teliospore, or more often the exospore ruptures and a thin-walled hypha 

 (promycelium) grows out into which the diploid nucleus passes. The 



