BRITISH FOREST TREES 85 



from branches, greatest quantitative production of wood and 

 of useful timber per acre, it is rivalled only by the silver fir. 

 Its crown is cone-shaped, and when grown in isolated 

 positions the whole foliage is retained in more or less conical 

 form from the summit downwards to near the ground ; the 

 short leaves or needles on the branches are retained for five 

 to seven years. 



Requirements as to Soil and Situation. Shallow-rooted 

 though the spruce undoubtedly be, yet it demands freshness 

 in the soil, and cool, damp, mountain atmosphere is bene- 

 ficial to its growth. Where other woods shelter it from the 

 wind it also finds a suitable abode in the vicinity of the sea- 

 coast, but its best development is attained in protected 

 localities on mountain sides. In its true home the average 

 temperature in July does not much exceed 66 Fahr. 1 and 

 the total minimum warmth requisite during each annual 

 period of active vegetation has been ascertained to be about 

 2,610 Fahr., which is about the annual average quantity of 

 warmth developed at latitude 69 north. Its growth seems 

 best when the enjoyment of the warmth, and thereby the 

 period of active vegetation, is confined to a short summer 

 season, during which there is daylight for the longest possible 

 time, as in the north of Scotland and in Norway and 

 Sweden. Drought is less easily borne by the spruce than 

 by any other tree. 



In regard to the quality of the soil, spruce shows a con- 

 siderable degree of indifference, or at any rate adaptability ; 

 it makes greater demands on mineral strength than the 

 Scots pine, but is content with less than the silver fir. 

 Being at the same time one of the thickly-foliaged species of 

 trees that improve the soil, and recruit such soils as have 

 become impoverished, it is frequently found where broad- 



1 Willkomm, Die forstliche Flora Deutsc/tlands nnd Oesterrtichs^ 

 887, p. 81. 



