THE RUSTS 



263 



This long life history, which is thoroughly known in Europe, 

 becomes much shortened in the Middle West, California, and 

 Australia, where there is no barberry, by the omission from 

 it of that host. In these regions the uredospores (summer 

 spores) may survive the winter or 

 dry season, or be carried over from 

 summer to summer through the 

 winter wheat and germinate di- 

 rectly upon the new developing wheat 

 of the following year, so that the re- 

 production of the rust is by a succes- 

 sion of the uredospores. 



There is no method known of killing 

 the wheat rust on the living host ; but 

 it has been found that certain varie- 

 ties of wheat, as the macaroni wheats, 

 are far more resistant to the rust than 

 others. There is some hope that varie- 

 ties may be bred by crossing our wheats 

 with macaroni wheat that will be 

 largely immune to this disease, which 

 annually causes losses of many million FlG - 233 - The summer spores 

 dollars in the United States alone. 1 tS3 ^ ^ "* 

 There are a large number of varieties A single twolLteieutospore, 

 of Puccinia graminis, and also several t, happens to be presentamong 

 other species of Puccinia which attack them ' ~ After De Bary 

 various grains, grasses, and other plants. One of these (P. as- 

 paragi) sometimes causes great damage to asparagus. 



Other rusts. The group of the rusts is very large, the genera 

 being distinguished chiefly by the structure of the teleutospores 



1 For a discussion of the rusts and rust problems of the United States, see 

 papers of Carleton from the publications of the United States Department of 

 Agriculture, "Cereal Rusts of the United States," Division of Vegetable 

 Physiology and Pathology, Bulletin 16, 1899 ; " Macaroni Wheats," Bureau 

 of Plant Industry, Bulletin 3, 1901; "Investigations of Rust," Bureau of 

 Plant Industry, Bulletin 63, 1904. 



