508 THE SMALL GRAINS 



of the plant, and, unlike those of the orange leaf-rust, are as abun- 

 dant on the culm and leaf sheath as on the leaf-blade. The teleuto- 

 sori soon become nearly as abundant as the uredosori, and burst 

 through the epidermis, causing a rough or ragged as well as black 

 appearance of the culm. 



Black stem-rust is the most destructive cereal rust in 

 this country, and sometimes ruins the crop completely. 

 In such cases either the spikes or panicles do not fill or 

 the kernels are so shriveled that the crop is not worth 

 harvesting. As this rust appears later than the leaf- 

 rusts, early varieties are likely to escape it. Rye and 

 barley, because of ripening early, are not injured so often 

 by stem-rust as wheat and oats. 



553. The crown-rust (Puccinia coronata, Cda.) is the 

 most common rust of oats, and corresponds to the orange 

 leaf-rust of other cereals. It is not found on any other 

 cereal. The crown-rust sometimes causes considerable 

 damage to oats, chiefly in hindering the elaboration of 

 plant-food in the leaves, but it is not nearly so destructive 

 as black stem-rust of oats. 



The secidial stage of the crown-rust is found on different 

 species of buckthorn. In this country one of the secidiai 

 hosts is Rhamnus lanceolata, as demonstrated by inocula- 

 tion experiments by the author (Carleton, 1900) . The ure- 

 dosori are light orange in color and are found chiefly on the 

 leaves. The teleutosori are subepidermal and have about 

 the same appearance superficially as those of the orange 

 leaf-rust. The teleutospores are crown-shaped at the 

 apex, hence the name of the rust. 



The crown-rust is found on several wild grasses, and is 

 often the only rust occurring on oats during the season. 

 It is injurious to about the same degree as the other leaf- 

 rusts. 



