644 THE PHYLOGENY OF THE FUNGI 



the water currents for their distribution sHp out from the tetrasporangium 

 as naked cells. 



Origin of Rusts and Smuts and Heterobasidiae 



As mentioned above, Jackson (1944) has emphasized the parallelism 

 of the life history types in the Uredinales and the Florideae. He has 

 demonstrated beyond chance of contradiction that the various types of 

 life history, such as alternation of haploid and diploid generations and 

 shortened life cycles occur in both groups of organisms, together with a 

 number of structural similarities (spermatia, receptive hyphae, etc.)- 



In view of the extreme, obligate type of parasitism of the rusts and the 

 usual nonparasitic mode of life of the red seaweeds, and of the type of 

 teliospores with promycelium — characters not indicated in the latter 

 group — it appears evident that the relationship is not necessarily very 

 close. Indeed the structure and function of these organs seem to indicate 

 relationship with the Basidiomyceteae under which they are more often 

 now classified. Bound up with the Uredinales is the question as to the 

 relationship of the Ustilaginales with which they have very often been 

 associated in classification. There is no denying the fact that in very 

 many regards the latter order is far less specialized in structure and life 

 history than the former. Yet there are a number of characters common to 

 both : (1) a high degree of intercellular parasitism confined to hosts among 

 the vascular plants; (2) a more or less well-marked distinction of two 

 types of mycelium, sometimes associated with special types of spores and 

 hosts, the monocaryon and dicaryon types of mycelium; (3) the produc- 

 tion on the dicaryon mycelium of binucleate cells, usually with colored 

 and thickened walls, in which the two nuclei unite ; (4) the outgrowth from 

 this teliospore of a thin-walled hypha (promycelium) of limited growth 

 within which meiosis occurs and upon which are then borne the sporidia 

 w^hich are of two or four sexual phases; (5) the production by the latter 

 of the monocaryon phase of mycelial growth; (6) the possession of various 

 methods by which this mycelium becomes diploidized to form the di- 

 caryon mycelial phase which produces the teliospores. Both orders give 

 rise to repeating spores, i.e., asexual spores which repeat the mycelial 

 phase upon which they are borne. In the Uredinales these are known onl,y 

 upon the dicaryon mycelium (being known as urediospores) but in some 

 of the Ustilaginales they occur on both monocaryon and dicaryon types 

 of mycelium. 



In some regards the Ustilaginales appear the more primitive in that 

 their dicaryon mycelium often has typical clamp connections, while these 

 have been definitely discovered in only a few cases in the Uredinales. In 

 the latter order there are present typically definite spermogonia which 

 produce spermatia capable of spermatizing receptive hyphae (tricho- 



