;6 DISEASES OF TREES 



in all directions, so that large branches may be eventually entirely 

 defoliated. In dense young woods it even spreads from branch 

 to branch, while fresh centres of disease are produced by the 

 distribution of the spores. 



Seeing that young woods which have been naturally regener- 

 ated may suffer severely and especially so where they have been 

 formed under shelter trees it is desirable that diseased branches 

 should be pruned off. This treatment has produced good results 

 where practised on a large scale. 



HERPOTRICHIA NIGRA * 



This parasite is met with in the higher mountain ranges, where 

 it chiefly attacks the spruce, mountain pine, and juniper. In the 

 woods of mountain pine, large blanks are met with, which, on a 

 cursory glance, give one the impression of having been completely 

 charred. In nurseries at high elevations, where the young spruces 

 are buried under snpw during winter and spring, it often happens, 

 directly after the snow has melted, that the plants are overgrown 

 and killed by the dark brown mycelium. This is especially notice- 

 able when the young trees have been laid prostrate on the ground. 



In the spruce woods of the Bavarian Forest one often finds 

 that the fungus has killed the young seedlings over large areas 

 either entirely or to the height of twelve or fifteen inches. The 

 dark brown mycelium envelops the whole branch or plant, knitting 

 the leaves completely together (Fig. 23). 



Instead of forming a definite cushion, the mycelium embraces 

 the leaves irregularly (Fig. 24, /?), and on these the perithecia 

 are also produced (a). Dark brown tuber-like bodies are formed 

 over the stomata (Fig. 25), while the mycelium also spreads 

 over the surface of the leaf and sends haustoria into the outer 

 walls of the epidermal cells, which consequently die and become 

 brown. The deeper-lying parenchymatous cells are also killed 

 by the fungus, even before any mycelial threads have gained an 

 entrance through stomata on other parts of the leaf, and pene- 

 trated into the interior. 



The surface of the dark brown comparatively large perithecia, 



1 R. Hartig, Herpotrichia nigra n. sp. All. Forst- und Jagd-Zeitg., 

 January 1888. 



