DAMAGE DONE. 665 



root to root of neighbouring trees and cause them to die in 

 groups. 



It is probable that when sound well-conducting trees 

 growing on damp soil are struck the lightning passes 

 rapidly down to the earth without causing much breakage, 

 but that when rotten wood is met with, which is a bad 

 conductor, the crown or branches may be broken, or even 

 the tree set on fire. 



The relative frequency with which trees are struck on 

 different soils in Lippe-Detmold is given below : — 



Loam 220 



Sand 118 



Clay 84 



Keuper marl .... 35 



Calcareous soil .... 28 



Flooded land .... 4 



This may explain the greater danger to trees from lightning 



in North Germany as compared with South Germany and 



Austria. It is also possible that loam and sand, producing 



most oaks and Scots pine, have high figures, while on 



calcareous soil the beech predominates. 



Trees are said to be more frequently struck by lightning in 

 badly wooded plains than in well-wooded mountain districts. 

 This is true for the bare middle Rhine valley and its adjoining 

 wood-stocked hills. 



It is supposed that dense forests act as conductors and 

 allow electricity to pass gradually from the earth to the 

 clouds, whilst clearing the land of forests increases the heat 

 of summer and hinders the neutralisation of the electricity of 

 the clouds. 



d. Density of Crop and Condition of Tires. 



Lightning, according to Hess, strikes in preference trees 

 standing free from their neighbours, those in avenues and on 

 the border of a wood and also trees dominating over the rest 

 of a wood. 



Sound trees are more frequently injured than unsound 

 trees, but dry trees may be struck, and stag-heacfed oaks 

 are frequently smashed to pieces by lightning. Thus, a 



