THE FUNGI WHICH CAUSE PLANT DISEASE 



359 



raphyses. The unicellular urediniospores are similarly surrounded, 

 and bear numerous germ pores. The genus is limited to Rosaceous 

 hosts and its species are autcecious. 



Eight American forms are recognized by Arthur ^* on roses as 

 follows: 



P. montivagum Arth., P. discifloruin (Tode) James, P. ameri- 



FiG. 261. — Uredinio- and teliospores of; 1. P. americanum; 2. P. roste-setigerse; 3. P. roaae 

 califomicse; 4. P. rosse-arkansanse; 5. P. montivaguin; 6. P. discifionun. After Arthur. 



canum Diet., P. rosse-setigerse Diet., P. rosae-californics Diet., 

 P. rosse-arkansanse Diet., P. subcorticinum (Schr.) Went, and 

 P. rosse-acicularis Siro. 



They are mostly on wild roses and of but little economic im- 

 portance. 



P. violaceum (Schul.) Went, is often serious on Rubus in 

 Europe. 



P. Tubi-idsei (Pers.) Wint. is found on raspberries in Europe. 



P. speciosum Fr. on rose has been separated by Arthur as 

 Earlea speciosa on account of its non-gelatinous teliospore pedi- 

 cel, its large compact caulicolous telia and the absence of uredinia. 



Gymnoconia Lagerheim (p. 355) 



0. Pycnia conic. 



I ( =Caeoma), peridia and paraphyses none. 

 III. Spores as in Puccinia. 



This genus bears a superficial resemblance to Puccinia but is 

 easily distinguished by its naked secial sori. 



