392 



UREDINEAE. 



than those of Cf. trerndloides. The aecidiospores Roestd'm 

 cornuta occur on species of Pyrus (Sorbvs); they are much 

 smaller than those of Roestdia pmifilhita. The Roestelia 

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

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

 Where Pyru-s Auc///>tiria occurs mixed with Pyrus Malus, 

 it has been observed that Roestdia eonmla is confined to the 

 former species exclusively. The Roestdia is the cause of 



a 



FIG. 225. Gymnosporangium juniperinum and 6?. trcmclloides. 1, Young spore- 

 cushions breaking through the bark ; 2, the same in swollen condition ; il, gela- 

 tinous cushion arranged to show its lower surface ; U, Juniper-needle with three 

 spore-cushions; /, young Juniper plant bearing cushions on its needles ; to 10, 

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

 wall ; 11, cell of a promycelium with a sporidium attached ; 1,.', germinating 

 spuridium. (After Tubeuf.) 



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

 fruits of Pyrus Aucuparia and Aronia rotnndifolia, both in 

 the lowlands and mountains. 



I have produced Roestdia cornuta on Pyrus Aucupciria by 

 artificial infection with portions of spore-cushions from twigs 

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

 with abundant Roestdia, directly beneath an overhanging juniper 

 with diseased needles. 



