ORIGIN OF RUSTS AND SMUTS AND HETEROBASIDIAE 645 



gynes) and thus diploidizing special cells from which are produced typical 

 dicaryon spores (aeciospores). In the Ustilaginales the diploidization may 

 occur in various ways but does not include spermatia and receptive 

 hyphae. 



If, then, the two orders Ustilaginales and Uredinales are considered to 

 be related we must conclude that they have arisen probably (1) from a 

 group of fungi in which clamp connections occurred or their homologues, 

 the croziers, characteristic of ascus formation; (2) from fungi in which 

 spermatia were produced in well-organized spermogonia; (3) from fungi 

 in which sexual reproduction was initiated by the spermatization of recep- 

 tive hyphae ; and (4) from fungi in which the monocaryotic and dicaryotic 

 mycelial phases were both present. Clamp connections are found in 

 most groups of the Basidiomyceteae and in some lichens while their 

 homologues, the croziers, occur in Lecanorales, Pezizales, Tuberales, 

 Sphaeriales, Aspergillales, and in the Ascocorticiaceae and a few other 

 forms. They are absent in the Laboulbeniales, Erysiphales, Saccharo- 

 mycetales, and a number of other groups. Spermogonia are found in 

 Laboulbeniales, Lecanorales, Sphaeriales, Pyrenulales, Dothideales, and 

 some Pezizales. Special receptive hyphae (trichogynes) are found in 

 Lecanorales, Pezizales, Laboulbeniales, Sphaeriales, Hypocreales, Py- 

 renulales, Dothideales, and a few other groups. The two mycelial phases 

 are absent in the Saccharomycetales and Taphrinaceae. We must there- 

 fore consider that the Rusts and Smuts may have been derived from some 

 Ascomyceteae possibly before the Pezizales, Sphaeriales, and Dothideales 

 had become strongly distinguished from one another. Possibly these early 

 ancestral Ascomyceteae if they were derived from Florideae that were 

 diplobiontic might have had their two mycelial phases much more 

 strongly marked than in the forms now known, in which the dicaryon 

 phase has been reduced to or has not yet proceeded beyond the formation 

 of the ascogenous hyphae. 



Linder (1940), in a very thought-provoking discussion, has sought to 

 derive the LTredinales from forms near the Dothideales. He assumed that 

 the disappearance of clamp connections or croziers may have been con- 

 nected with the parasitism entirely within the host tissues. He believed 

 that the Ustilaginales (which still retain clamp connections) were derived 

 from the Uredinales with reduced life cycles in which loss of spermatia and 

 receptive hyphae had been recompensed by the ability of any two cells of 

 opposite sexual phase to fuse and thus initiate the dicaryotic type of 

 mycelium. It must be remembered that even in the Uredinales there 

 appears to develop mutual diploidization of mycelia of opposite sexual 

 phase when they meet in the tissues of the host, even though spermatiza- 

 tion of receptive hyphae is prevented. 



Linder's view of the origin of the teliospore and promycelium from the 



