CEREAL PESTS PARASITIC FUNGI 507 



of the leaves in the elaboration of food material. It is 

 rarely or never so destructive, however, as the black 

 stem rust. 



551. The dwarf rust (Puccinia simplex, Eriks. & Henn.) 

 appears superficially much like the preceding, occurring 

 chiefly on the leaves. It is not common, and is found only 

 on barley. The uredosori are orange colored. The 

 secidial stage, if any, is unknown. The teleutosori are 

 subepidermal, as in the preceding, and occur most abun- 

 dantly on the leaves. The teleutospores are dwarfed and 

 usually only 1 -celled. 



552. The black stem-rust (Puccinia graminis, Pers.). 

 -This rust is apparently found in all countries, but is 



much less common and abundant than the orange leaf- 

 rust, and is often absent the entire year in- some localities. 

 In some places in this country, it is seldom or never seen 

 on certain hosts. In North America the species attacks 

 wheat, oats, barley, rye, and many wild relatives of these 

 cereals. 



Inoculation experiments by the author (1889, pp. 52- 

 65) indicated that there are at least 2 physiologic forms 

 of this rust on cereals in the United States, one on oats, 

 and one on wheat and barley, with probably a third form 

 on rye. Eriksson (1896) determined that in Sweden there 

 are 3 forms, one on oats, one on wheat, and a third on 

 rye and barley. Later, Freeman and Johnson (1911, 

 p. 27) decided that there are 4 forms, one on wheat and 

 barley, a second on rye and barley, a third on wheat, rye, 

 and barley, and a fourth on oats. 



It is well known that the aecidial stage of this species occurs on 

 the barberry. It is not of general occurrence in this country, 

 however, but is occasionally fairly abundant in a particular locality. 

 The uredosori are a dark brick-red or brown and occur on all portions 



