384 



THE FUNGI WHICH CAUSE PLANT DISEASE 



P. simplex (Korn.) Er. & He. 



I. Unknown. 



II and III on barley in Europe and seemingly of recent intro- 

 duction into the United States.'*"^ 



One of the least important of the grain rusts. Mesospores are 

 common. 



P. sorghi Schw.^s" 



I (=^. oxalidis). Peridia hypophyllous, rarely amphigenous, 

 crowded, concentric, epispore smooth, 24-28 fi. 



II. Uredinia amphigenous, numerous, often confluent; spores 

 globose to ovate, 23-30 x 22-26 mm., slightly verrucose. 



Fig. 277. — Puccinia aorghi. After Scribner. 



III. Telia amphigenous, black. Spores ovate-oblong or clavate- 

 obtuse, constricted. Epispore thick, 28^5 x 12-17 m, smooth, 

 pedicel long, 5 ix, persistent. 



Heteroecious. O and I on Oxalis. II and III on Zea. Of little 

 economic importance. 



The relation of the fecial stage was demonstrated by Arthur; '^ 

 it is beheved, however, that hibernation is largely by the uredinio- 

 spores. 



P. purpurea C. Amphigenous, spot purplish, sori irregular, 

 dark-brown. 



II. Urediniospores ovate, 35 x 25-30 /j, smooth, brown. 



III. Teliospores elongate, ovate, brown, long-pedicellate, 40^5 

 X 22-25 M- On Sorghum in Southern United States and West 

 Indies. 



