378 



UREDINEAE. 



and small yellow pycnidia are produced during July or 

 August. The aecidia follow from August till September, 

 occupying yellow zones on the otherwise green needles ; their 

 white peridia project as much as 2 mm. above the surface of 

 the needle, and dehisce by rupture of the apex. The aecidiospores 

 are formed in large numbers and, carried by wind, reach leaves 

 and shoots of alpine-rose where they immediately germinate. 

 The resulting mycelium produces in September yellow clusters 

 of uredospores on brownish spots on the lower epidermis of 

 the leaves, and on the bark of last year's shoots (Fig. 210). 



FIG. 209. Chrysomyxa rhododendri. Twig 

 of Rhododendron hirsutv.m with sori of uredo- 

 spores on the lower epidermis, causing dis- 

 coloured spots on the upper, (v. Tubeuf 

 del.) 



FIG. 210. Ckrysomy.ca rhododendri on Rho- 

 dod< ndrou fn-i-ugineum. Uredospore-sori in 

 September as elongated white stripes on the 

 stem below the leaves, (v. Tubeuf del.) 



The uredospores are yellow and ovoid, with granular protuber- 

 ances on their coats ; they are developed in series from the sori. 1 

 The disease may be further propagated during the same year 

 by the uredospores. In districts where spruce does not occur, 

 it is probable that these spores hibernate, and in the following 

 spring produce germ-tubes which infect other alpine-rose leaves. 

 It frequently happens that whole forests of spruce are so attacked 

 by this fungus that many of the trees retain only a few 

 healthy needles. Diseased needles die and fall in the summer 

 of attack, so that the trees may be almost wholly stripped, 

 and thereby suffer considerable damage. 



Chr. ledi (Alb. et Schwein.) 2 (U.S. America). This fungus 



1 Raciborski regards the Uredo as a Caeoma-form. 

 2 De Bary, Botan. Zeitumj, 1879. 



