1920.] 



Scorch I NCI of Foliacje. 



18B 



to mechanical injuries.* Damage of this kind, of course, occurs 

 during gales, but, in the region referred to, Hansen's observa- 

 tions! indicate that the drying action of storms and of long- 

 continued winds causes injury to a much greater extent, and the 

 same relation is probably of general application. Borggreve 

 refers to the question of injury by salt, and states that storms 

 from the sea on the Baltic coast as a rule only carry small quan- 

 tities of salt. He also contends that trees protected by buildings, 

 embankments, hedges, &c., would be equally or more exposed 

 to salt than those standing without protection, because heavy 

 particles suspended in the air would tend to be deposited where 

 the air is less vigorously moved. The argument, however, is a 

 superficial one, and is unsupported by direct observation cf the 

 distribution of salt under the conditions referred to. In com- 

 paring an exposed and a partially protected situation, one would 

 probably be much less concerned with the settling down of salt 

 particles owing to their weight than with the relative (juantities 

 of salt brought into contact with foliage by the wind in a given 

 time, the salt being frequently either contained in spray, or 

 brought in the form of damp particles which would adhere to 

 anything they touch, while the amount of salt arriving in a 

 given time would be decreased, wherever the velocity of the wind 

 is reduced. On the other hand it may be supposed that, in the 

 special case of a very heavy spray being carried by a wind, the 

 unprotected external foliage of trees may become so wet that the 

 salt water, dripping on or blown on to the leaves of the interior of 

 the crown, may eventually expose many of these to about the 

 same amount of salt as that remaining on the exposed leaves. 

 In the absence of definite data, however, it is inadvisable to base 

 an}" argument on this supposition. 



Before considering the manner in which salt might occasion- 

 ally be a contributory cause to damage, some further remarks on 

 the action of wind should be made. The effect of wind in causing 

 loss of moisture from foliage by transpiration will depend on 

 both the degree of dryness and the velocity of the wind. Dry 

 air naturally favours transpiration, and wind in most cases has 

 the same effect. In still air the water-vapour transpired by a 

 leaf accumulates to some extent in its vicinity, thus checking 

 transpiration, while during a wind the vapour-laden air is con- 

 tinually removed, so that the leaf transpires actually into drier 



* Such as bruisint; ami breaking of branches and leaves. Mechanical injuries 

 may perhaps be caused by wind-blown sand in certain localities (see Gerhardt, 

 loc. fit.), bit probably chiefly to yountr leaves of shrubs. 



f Hansen, T'cv;. ostfries. Ins''ln, )>. 'M\. 



