262 PLANT DISEASES 



of living leaves of groundsel {Senecio vulgaris)^ ragwort 

 {Senecio Jacobea), and various other species of Se7iecio. The 

 aecidia are of two forms, one cylindrical and slender, formed 

 on the leaves; the other much larger and inflated, growing 

 in crevices of the bark of Pmus silvestris, P. mariti??ia, 

 P. ins ignis, and P. strobus. 



Preventive Means. — The injury done is slight, mostly 

 amounting to a discoloration of the leaves, which, however, 

 do not fall before the normal time. The removal of species 

 of Se?iecio from the neighbourhood arrests the disease. 



RHODODENDRON RUST 



i^Chrysomyxa rhododeiidri, De Bary.) 



This fungus is heteroecious, the uredo and teleutospore 

 stages occurring as small pustules on the leaves of species 

 of Rhododendron, R. hirsutum, and others ; w^hereas the 

 aecidium stage grows on the young shoots and leaves of 

 the spruce. Yellow spots appear on the spruce leaves, 

 and about August the spermogonia of the fungus appears 

 on these spots ; at a later period numerous peridia are 

 produced, and contain such a quantity of spores that when 

 a diseased tree is shaken the air is filled with a dense 

 cloud of spores. Diseased leaves die and fall the same 

 season. 



In the present genus the teleutospores consist of a row 

 of superposed cells. Not a dangerous parasite. The 

 removal of either of the hosts from the vicinity of each 

 other checks the disease. 



De Bary, Bot. Zfg., 1879. 



Hartig and Somerville, Diseases of Trees, p. 177. 



