392 



UREDINKAE. 



than those of G. tremdloides. The aecidiospores — Boestelia 

 cornuta — occur on species of Pyrus {Sorbiis); they are much 

 smaller than those of Roestelia penicillata. The Hoestelia 

 themselves are long, curved, and hom-like, while the walls of 

 the peridial cells are beset with short processes (Fig. 224). 

 Where Pynts Aucuparia occurs mixed with Pyrus Malus, 

 it has been observed that Boestelia cornuta is confined to the 

 former species exclusively. The Eoestelia is the cause of a 



Fig. 225. — Qy-innoiporaTigiutn. jv.niperinv.m and G. tvanelloides. 1, Young spore- 

 cuflhions breaking through the bark ; S, the same in swollen condition ; 5, gela- 

 tinoiis cushion arranged to show its lower surface ; 4, Juniper-needle with three 

 spore-cushions ; 5, young Juniper plant bearing cushions on its needles ; 6 to id, 

 spores of various lands, to show the variation in size, shape, and thickness of 

 wall; lly ceil of a promycelium with a sporidium attached; IS, germinating 

 sporidium. (After Tubeuf.) 



marked deformation of leaves, petioles, and even (though rarer) 

 fruits of Pyrus Aucuparia and Aronia rotundifolia, both in 

 the lowlands and mountains. 



I have produced Roestelia cornuta on Pyrus Aucuparia by 

 artificial infection with portions of spore-cushions from twigs 

 of juniper, and have observed a mountain ash in closed forest, 

 with abundant Roestelia, directly beneath an overhanging juniper 

 with diseased needles. 



