424 CLASS BASIDIOMYCETEAE 



come in contact within the host but the usual mode of reproduction is by 

 the union of sperm cells with special receptive hyphae of the opposite 

 sexual phase. The Rusts have reached a much higher stage of specializa- 

 tion of spore forms and of adaptation to alternate hosts, while the Smuts 

 are parasitic but able to grow saprophytically, thus eliminating the neces- 

 sity for two growth phases in the same or different species of hosts. Be- 

 cause of the formation of sperm cells in typical spermogonia and the pro- 

 duction of receptive hyphae the Rusts in this regard hark back to more 

 primitive ancestral forms among the Ascomyceteae where such struc- 

 tures are present. Clearly the Ustilaginales must have branched off from 

 the earlier Rusts, with loss of these special organs, but at an early stage 

 when the inherited tendency to produce clamp connections had not been 

 lost. Jackson (1931) points out the similarity in life cycles of many Rusts 

 and Florideae. This is worthy of further careful consideration. The rela- 

 tionships of the Teliosporeae to the Subclass Heterobasidiae are discussed 

 in the next chapter. 



Key to the Orders and Families of Subclass Teliosporeae 



Obligate parasites in Pteridophyta, Strobilophyta (Coniferae) and Anthophyta 

 (Angiospermae) . Teliospores single or united into crusts or columns or 

 several together in compound spores, remaining within the host tissue or 

 bursting through the epidermis or cuticle. Spermogonia normally produced, 

 the sperm cells diploidizing special receptive hyphae. Typically three types of 

 spores are produced, aeciospores, the product of the diploidization of mono- 

 caryon mycelium which arises from the sporidia; urediospores (repeating 

 spores) and teliospores from which arise the promycelia and sporidia. Sporidia 

 always expelled violently. Order Uredinales 



Teliospores without stalks, produced singly or in groups of two to four in the 

 mesophyll or just below or within the epidermal cells or united laterally into 

 subepidermal or subcuticular crusts or united into separate vertical chains 

 or into chains that are joined laterally into a waxy column which emerges 

 through the epidermis. Aecia mostly on species of Pinaceae. 



Family Melampsoraceae 



Teliospores usually stalked, simple or compound, sometimes without stalks and 

 produced successively as simple or compound teliospores which escape from 

 the sorus dry or embedded in slime. Aecia only very exceptionally produced 

 on Pinaceae. Family Pucciniaceae 



Obligate parasites in Anthophyta or in many cases facultative saprophytes. Telio- 

 spores single or united in columns or balls, remaining within or bursting out 

 of the host tissue, mostly distributed by air currents. No spermogonia or 

 special receptive hyphae. Diploidization by means of union of compatible 

 spores, hyphae, etc. Typically only teliospores and oftien hyaline thin-walled 

 conidia are produced. Sporidia expelled violently in one family, not so in the 

 two others. Order Ustilaginales 



Promycelium transversely septate into several, mostly four, cells. Teliospores 

 arising in the tissues of the host from transformed hyphal cells, and mostly 

 distributed by air currents. Sporidia not expelled from the promycelium. 



Family Ustilaginaceae 



