414 FUNGOUS DISEASES OF PLANTS 



solved. The rust may appear, or seem to appear, in constantly 

 increasing amount in a field repeatedly grown to wheat, other con- 

 ditions apparently remaining the same, yet it is hardly possible to 

 assume that wintered uredospores would explain such cases. 



The teleutosori are generally disposed in a linear manner on 

 stems, leaves, and floral parts. They may arise, during the early 

 part of the season, in the uredosorus, but as the plant matures, 

 teleutospores alone are developed ; thus the black rust form is that 

 most evident at harvest time and later upon the stubble. In gen- 

 eral, the spores are somewhat spindle-shaped, or somewhat broader 

 at the apex, deep brown in color, with a persistent pedicel (Fig. 

 203, ). They measure 35-60 x 12-22/x. One-celled spores are 

 occasionally found. The teleutospores will not, as a rule, germi- 

 nate with any degree of satisfaction until they have been exposed 

 to outside conditions throughout a considerable portion of the 

 winter. Germination has, however, been repeatedly followed, and 

 in moist air the promycelium is typically four-celled, each produc- 

 ing upon a fairly long sterigma the single sporidium (Fig. 203, b). 



XIV. RUST OF MAIZE 



Pucdnia Sorghi Schw. 

 ARTHUR, J. C. The yEcidium of Maize Rust. Bot. Gaz. 38: 64-67. 1904. 



It is generally supposed that this fungus is a native of America, 

 and that it may be regarded, so to speak, as an original corn (Zea 

 mays} parasite. It is now certainly widely distributed in maize- 

 growing regions, but is more abundant under conditions of rela- 

 tively high temperature. This fungus has also been reported on 

 sorghum, but the maize fungus is distinct from Pncciniapnrpnrca, 

 now common in the southern United States and in the West Indies 

 on certain species of sorghum. The uredospores are large, 23-30 

 X 22-26 /A, and the teleutospores are smooth, 28-45 X 12 - 1 7/ JL , 

 with a rather long and thick pedicel. 



On maize the rust affects particularly the leaves and leaf 

 sheaths, but it may cause considerable damage to the develop- 

 ment of the tassels. Nevertheless, it seldom amounts to an 

 epidemic, and consequently has not received attention from the 

 standpoint of control, or of varietal selection of the host. 



