74 THE BUSTS OF GRAINS IN THE UNITED STATES. 



is almost always virulent on the coast of California, and is severe and 

 frequent in the southern half of Texas. The epidemic of 1904 was 

 prevalent throughout the entire Mississippi Valley, extended into the 

 wheat fields of the Canadian Northwest, and even invaded the drylands. 



Leaf rust of wheat is also coextensive with the wheat crop and is 

 more common in many districts than stem rust. It occurs yearly 

 over the eastern half of the United States. The losses caused by it 

 are not comparable to those caused by stem rust. 



Stem and leaf rusts of oats are coextensive with the oat crop. 

 They usually occur together and are abundant east of the dry belt of 

 th? Great Plains region, are paramount in importance in the South- 

 ern States, and extend north to the Canadian border and even beyond. 



Stem rust of barley is practically coextensive with barley, but is 

 not often present in sufficient quantity to do serious damage. 



Leaf rust of barley seems to be of recent introduction. It is eco- 

 nomically one of the least important of the grain rusts. 



Stem rust of rye is probably widely distributed in small quantities 

 and is fairly common, but causes little injury. 



Leaf rust of rye is widely distributed and very abundant, but 

 causes little damage, as the rust is closely confined to the leaves and 

 the rye matures too early to be appreciably damaged. 



(3) Botanical characteristics, life histories, and physiological spe- 

 cializations of parasitic fungi may vary with the geographical distri- 

 bution. European and American forms may be apparently identical 

 morphologically, but are not necessarily identical in their life histo- 

 ries or physiological specialization. 



That stem rusts on wheat, rye, oats, and barley, both in Europe and 

 America, may produce their secidia on barberry has been proved, but 

 that they always do so and can not live for more than one season with- 

 out passing on to barberry is disproved by experiment. 



The secidial stage of leaf rust of wheat is not known either in 

 Europe or in this country. The uredo stage exists through the winter 

 months, and the rust may live independent of an secidial stage. 



The secidial stage of the crown rust of oats occurs in Europe on 

 Khamnus frangula L. and R. cathartica L. and in the United States on 

 R. lanceolata Pursh., R. caroliniana Walt., and R. cathartica. 



The secidial stage of the leaf rust on rye occurs in Europe on 

 Anchusa officinalis L. and Lycopsis arvensis L. It is believed that 

 the European and American forms are identical. 



The secidial stage of the leaf rust on barley is not known for Europe 

 or America. This rust seems not to have been previously reported 

 in this country. 



Rusts exhibit great variety in regard to complexity of life histories; 

 some are confined to a single host species, some range over two or 



216 



