408 



UREDINEAE. 



cone rust. This disease is found on the cones of spruce. 

 The aecidia are brown somewhat flattened spheres, and appear 

 in large numbers on cones distinguished by their scales standing 

 stiffly open even in damp weather (Fig. 243). The germ- 

 tubes of the fungus find entrance in spring into the flowers 

 or young spruce-cones, and the mycelium lives parasitic in 

 the green scales without causing any marked change in 

 their growtli, although the ovules are more or less injured. 

 Xo mycelium has ever been found in the lower cone-axis, nor 

 in the shoots, so that the disease nnist be tlie result of in- 

 fection l)y spores only. 



-I 





2 3 



Fig. ^ii. —Aecidium HivhUinum. 1, Cone-scale of Spruce with aecidia, tliose to 

 left dehiscing their yellow spores, those to right still closed, (v. Tubeuf del.) 

 2, Section through an immature aecidium. 3, Part of 2 enlarged— y)ir, peridium ; 

 .«/), spores; zto, intermediate cells; sptr, sporophorcs ; m, mycelium; im,; the 

 scale-parenchyma. (After Reess.) 



\ 



The aecidia break out on the inner (rarely the outer) side 

 of the bases of the cone-scales ; each is enclosed in a firm 

 brown lignified peridium, which ruptures by a cross-fissure 

 and becomes an open disc. The young spores are joined by 

 small intermediate cells, which are gradually absorbed to 

 form a layer of gelatinous lamellae on the spore-coats 

 (Fig. 244). 



Teleutospores of this Acctdium are unknown. 



