664 PROTECTION AGAINST LIGHTNING. 



In the Saxon State forests, in 1897, the first year that such 

 observations were made, it was found that the danger for oak 

 was six times that for conifers. 



On the whole, from these observations it is evident that 

 local circumstances such as proximity of lakes, dampness of 

 soil, density of growth, healthy or unhealthy condition of 

 trees, affect the question whether one species will be more 

 liable to attack than another in any particular locality. 



Some experiments as regards the conductivity of electricity 

 by wood have been recently made by Jonesco, of the Wiirttem- 

 berg Society of Natural Science. In these experiments Holz's 

 electric machine was used. 



1 turn passed the spark through oakwood, 



12 to 20 turns through beech, 



5 turns through poplars and willows. 



The use of heartwood or sapwood and state of dryness of 

 the wood made no difference in the results, but the richness 

 of beech in oil prevents its being a good conductor. 



Fischer ("Biologic der Holz Gewachse"*) distinguishes 

 between oily trees and starchy trees. In oily trees, the elaborated 

 starch, during winter and spring, becomes converted into oil and 

 passes into the pith, wood, and bark. Part of the starch in the 

 bark also becomes converted into glucose. In the starchy 

 trees, the reserve starch remains unaltered between autumn 

 and May. 



The green wood of the oily trees (beech, walnut, birch, 

 lime), especially wood very rich in oil, is a bad conductor of 

 electricity. The starchy trees (oak, poplar, maples, ash, elm, 

 sorbus) are good conductors. Conifers are intermediate, the 

 Scots pine in summer being as poor in oil as the starch trees, 

 but rich in oil during winter. After the oil had been extracted 

 from wood of fatty trees by means of ether they became as 

 good conductors as typical starchy trees. 



Starchy trees are therefore more in danger from lightning than 

 oily trees. 



c. Locality. 



Damp soils conduct electricity well, but in dry places when 

 the lightning has reached the ground, it may spread from 



* Pringsheim'a ' Jahrbuch fur wisserischaftliche Botanik," Band xxii., p. 73. 



