INJURIES INDUCED BY PLANTS 



77 



Fig. 24, is beset with numerous branching hyphae, which are 

 specially abundant on the lower part, near the point of contact 

 with the mycelium. These black spheroid bodies are frequently 

 nearly hidden by the mycelium. In the asci the spores are 

 arranged in two rows. At first, and apparently also when 

 mature, they consist of two chambers, but at last four chambers 

 are formed. These spores germinate with great readiness. 



It is an interesting biological point that the fungus grows, es- 

 pecially when the temperature is low, 

 under the snow or during the time it 

 is melting, because, under such cir- 

 cumstances, the air is completely 

 saturated with moisture. The fre- 

 quency of the disease at high eleva- 



FIG. 24. a and b t two spruce 

 leaves attacked by H. nigra, 

 twice natural size. The brown 

 mycelium forms black tuber- 

 like bodies in the stomata, 

 which however are much 

 smaller than the black peri- 

 thecia, one of which, magni- 

 fied fifty times, is shown in 

 the lower part of the figure. 



FIG. 25. The growth of the mycelium 

 of H. nigra. The filamentous my- 

 celium a develops a granular mycelium 

 on the surface of the leaf, and this 

 covers the stomata with tuber-like 

 bodies, rod-like haustoria being sent 

 into the outer walls of the epidermal 

 cells. 



tions has led to the general adoption of the practice of forming 

 spruce nurseries at low altitudes. It has also been found a 

 good plan to look over the nurseries immediately after the 

 melting of the snow, and to raise up all prostrated plants in 

 order that they may be exposed to the wind. It would also 

 be a step in the right direction, in planting out trees, to set 

 them on hillocks and similar elevations, and to avoid placing 

 them in hollows and other depressions. 



