396 CLASS BASIDIOMYCETEAE 



wintering wheat or rye or other grains. In the southern portions of the 

 United States and Europe the rust is not killed out by the cold of winter 

 and so perpetuates itself by its urediospores. Under such conditions the 

 eradication of the barberry has little effect. The apple rust has been found 

 to be susceptible to control by removal of its alternate host, the red cedar, 

 over an area to a distance of a mile or more from the orchard that is to be 

 protected. White pine blister rust requires the destruction of all currants 

 and gooseberries to a distance of half a mile (one mile for Ribes nigrum L.) 

 from the trees it is desired to protect. Puccinia ruhigo-vera tritici, although 

 heteroecious, cannot be controlled in this manner for the rust that infects 

 the wheat in the fall survives the winter on this host and produces uredio- 

 spores in the spring from which the disease is spread. In fact this rust is 

 exceedingly abundant in many parts of the United States where the host 

 for the aecial stage does not occur. 



The rust life cycle described above is the typical one. Rusts possessing 

 such a cycle are called macrocyclic or long-cycle rusts. Arthur and his col- 

 laborators (1929), Jackson (1931), and others believe that these represent 

 forms with the more primitive life cycle so far as present rusts are known. 

 Many species of rusts have shortened their life cycle by the omission of 

 one or more stages. Dietel (1928), Olive (1908), and Grove (1913), on the 

 contrary, consider the forms with the short life cycle to be more primitive. 

 As examples of the omission of certain stages the following may be men- 

 tioned. Most species oi Gymnosporangium produce no binucleate repeating 

 spores (urediospores) from the dicaryon stage of growth but they do occur 

 in G. nootkatense (Trel.) Arth. Some rusts produce only spermogonia and 

 telia while still others omit the spermogonia also (e.g., Puccinia malva- 

 cearum Bert.). These last two are properly speaking microcyclic rusts. 

 There are also rusts in which no true telia are produced but whose aecio- 

 spores germinate in the manner of teliospores by the formation of a 

 promycelium. These rusts also are microcyclic. Kunkelia nitens (Schw^) 

 Arth., on Ruhus spp. is of this type as are the various species of Endo- 

 phyllum. The microcyclic species are of especial interest as regards the 

 origin of the binucleate condition of the young teliospore. In Puccinia 

 arenariae (Schum.) Wint., liindfors (1924) described the formation of a 

 two-celled promycelium, each cell giving rise to a binucleate sporidium. 

 This produces a dicaryon mycelium and no monocaryon mycelium occurs. 



Another anomaly in the life cycle of a short-cycle rust is described by 

 Thirumalachar (1946) for Uromyces aloes (Cke.) Magn. In this species the 

 spermogonia appear to be normal and exude drops of sweet liquid filled 

 with sperm cells. However, there are no flexuous hyphae. The appearance 

 of the spermogonia is followed immediately by the development of teha. 

 The monocaryon mycelium within the sorus shows here and there con- 

 tacts between two adjacent hyphae where the intervening walls are dis- 



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