CHAP. VIII MOVEMENTS OF THE AIR 37 



Eminently worthy of note is the significance of the f ohn-vvind ^ to 

 vegetation. The valleys where the fohn prevails are well known for 

 the vegetation, which is that of a warmer chmate. 



In places sheltered from the wind the vegetation shows a development 

 different from that in unsheltered situations. Wind, when strong and 

 much inchned to prevail in one direction, exercises a remarkable influence 

 on the form of tree-growth and on the whole character of the landscape. 

 Distorted growth and nanism are the consequence. Trees display the 

 following peculiarities in shape : 



(i) They are low in stature. 



(ii) The trunk is often bent in the direction towards which the pre- 

 vailing wind blows, and the boughs are curved and bent in the same sense. 



(iii) The shoots are short, often irregularly branched and interlaced. 



(iv) Many shoots are killed on the windward side, and sometimes 

 one finds new shoots and fresh leaves only on the lee-side. 



(v) The crown assumes a peculiar shape by unilateral branching 

 (Picea excelsa), or, because it inchnes from the windward side, appears as 

 if clipped and rounded off, and exposes a very close-set surface.^ 



(vi) The whole forest or bush-wood inclines in like manner away from 

 the windward side. 



(vii) Sometimes on the most exposed side the shoots springing from 

 the root or from the base of the stems are the only ones to maintain a 

 fair existence : so that on the windward side a forest may dwindle to 

 scrub, and this in turn may be resolved into scattered or isolated cushion- 

 like individuals (e. g. on the heaths of Jutland). 



(viii) The leaves become smaller than usual, and often are more or 

 less brown in patches, or reddish (as if burnt), particularly at the margins. 



Like effects of the fohn-wind in East Greenland, on dwarf shrubs 

 and perennial herbs, have been described and figured by Hartz ^ ; in this 

 case the masses of sand and stone carried by gales have an erosive and 

 destructive influence on the windward side.* 



Various explanations of the effects of wind have been given : 



Borggreve assumed that all effects are essentially due to the mechanical 

 action of wind, in that the shoots and leaves are beaten against one another, 

 shaken, rubbed, and lashed. It is certain that wind can exert a direct 

 mechanical action upon plants, and, for example, cause trunks of trees to 

 slope and their branches to be eroded and barked. 



Other authorities ascribed to wind an indirect physiological action of 

 some kind or other. 



Focke expresses the opinion that the injuries done to plants may 

 be wrought by particles of salt conveyed by sea-breezes, but the same 

 changes in form are to be observed far inland : for instance, in oak- 

 scrub in central Jutland, or in the centre of Switzerland. 



Still others regarded cold as the cause, but on tropical coasts, for 

 instance in the West Indies and at the mouth of the Amazon, we note, 

 under the influence of the trade-wind, the re-appearance of shapes identical 

 with those of our own latitudes, and the cessation of the effects of the 

 wind when any sheltering object intervenes. 



' In regard to the theory of the fohn-vvind consult Hann, 1897. 

 ' Friih, 1901 ; Klein, 1899, 1905. * Hartz, 1895. 



' See also Bematzky, 1901. 



