Oct. IS, 1921 Aecial Stage of the Orange Leaf rust of Wheat 153 



Rumex acetosa, and Urtica dioica. These results substantiate those 

 obtained by Eriksson and indicate that the positive results reported by 

 Nielsen {20) and Plowright {21) were probably due to a mixture of rusts 

 or of hosts. 



The failure to obtain infection on Boraginaceous hosts has influenced 

 other workers to turn their attention to other families in a search for the 

 aecial hosts. Arthur (j, v. 9, p. 304), largely as a result of morphological 

 studies, reached the conclusion that Puccinia triticina was best con- 

 sidered a race of P. Agropyri, and upon this basis Arthur and Fromme 

 (j. P' 333~337) have placed it in the collective species Dicaeoma Clerna- 

 tidis (DC.) Arth. Several races of this collective species had been shown 

 by workers in Europe and America to go to species of Clematis. Arthur 

 thought that the aecial host might be either Clematis ftamm.ula or C. 

 vitalha as these were the only common species of Clematis found in the 

 wheat-growing regions of southern Europe, northern Africa, and western 

 Asia, a region which at that time was considered as the probable home 

 of the original wild wheat. His culture with wintered telia of the leaf- 

 rust of wheat on C. flammula, however, was unsuccessful. 



According to Butler (d, p. 75) Cunningham and Prain (9) considered 

 that there was considerable ground for believing that an Aecidium on 

 Launaea asplenijolia, one of the Cichoriaceae, was the aecial stage of 

 Puccinia triticina, as it was found throughout the greater part of the 

 wheat-growing area of India. Butler, however, sowed aeciospores from 

 this host upon wheat without obtaining infection. 



These unsuccessful attempts to demonstrate an aecial stage for Puc- 

 cinia triticina have resulted in the development of the idea that the 

 aecial stage of this rust has been lost and that it is able to maintain itself 

 without one. In this connection a number of important facts have 

 been established and a number of interesting hypotheses proposed. It 

 has been shown by BoUey (5, p. 13-14), Hitchcock and Carleton (15, p. 

 1—2), Carleton {8, p. 21-22), and others that in certain regions, P. tri- 

 ticina is able to overwinter by means of its uredinal mycelium and that 

 no aecial host is necessary for the maintenance of this species. This 

 does not appear, however, to be true for all regions where P. triticina is 

 abundant {6, p. 11). A number of suggestions have been made to ex- 

 plain the 5'early appearance of the rust in regions where the uredini- 

 ospores or uredinial mycelium does not overwinter. It was considered 

 possible that spores may be carried from other regions by the wind. 

 The mycoplasm theory of seed transmissal has also been put forward as 

 a possible explanation. Whatever may be the merits of these hypothe- 

 ses, they have resulted in recent years in directing attention away from 

 a search for the aecial host of this species. 



