Chai\ I] THE FORMATIONS 171 



fatal level. As the juniper has absolutely no power of emitting suckers from its 

 roots or even supplementary shoots from the base of the stem, there results a 

 low tabular little tree, whose dense umbrella-shaped crown attains a diameter 

 of 3-4 meters, and whose central cylindrical stem at an age of 300-400 years 

 may have a diameter of more than thirty centimeters. The height of the whole 

 plant is, on the average, about 1 meter, but may occasionally reach nearly 

 2 meters. ... If the little stem, which is in great request as firewood, 

 should remain standing long enough, there comes, sooner or later, a moment 

 when the adherence of the roots to the soil can no longer resist the increasing 

 pressure upon the crown by the wind ; the little tree falls over and is obliquely 

 held up by the half of its crown that is now turned downwards, whilst its 

 upper half quickly dies off and disappears along the critical line. 



' The line above which all twigs perish is defined by the average height of 

 the snow-covering at the commencement of the thaw. ... In April, 1889, 

 I was able to satisfy myself that the living juniper branches reached close up to 

 the surface of the melting snow, or that at the most they projected a few 

 centimeters above it. I have convinced myself that the juniper in Russian 

 Lapland can withstand the winter only if for several months it is completely 

 covered with snow 1 . . . . The birch also assumes the form of tabular or 

 closely cropped bushes, which are quite characteristic of the tundra landscape, 

 in accordance with the wide distribution of this tree beyond the limit of forests V 



Finally, as an extreme case, Kihlman mentions the formation of mats, ' that 

 merely reach the height of the surrounding felt of lichens or undershrubs, but 

 which occasionally attain quite considerable dimensions in the horizontal plane. 

 . . . The shallow-rooted spruce assumes this form most successfully (Fig. 92) ; 

 along the tundra belt near Orlova I saw mat-like spruces from one to five 

 meters long, the thin sterile twigs of which had crept about in the felt of lichens 

 and evidently all sprang from one seedling plant. ... In all these mats one 

 finds that the one-year-old shoots, in so far as they project above the level of the 

 surrounding tufts of moss and lichens, are dried up and defoliated V 



As will be shown in a later chapter 4 , the conditions in regard to the 

 movements of the air also determine the vertical limit of forest vegetation. 



It appears to be advisable to group together shrubs and divarf-trees as 

 brushwood. 



The existence of brushwood also is determined by the amount of water 

 in the soil, and the season when the water is renewed is a matter of in- 

 difference. The amount of water necessary for the well-being of brush- 

 wood is less than that for tree-growth ; when it increases, tree-growth 

 appears. Like forest, brushwood thrives better in damp than in dry 

 air, and better in calm than in agitated air ; in both respects, however, 

 it is more accommodating than is tree-vegetation. 



A good woodland climate is, tJien, composed of the folloiving elements : — 



1 Kihlman, op. cit., p. 71. 2 Id. p. "]?,. 



3 Id. p. 68. 4 In Part III, Sect. IV. 



