7 



ELECTRICAL RESISTANCE OF TREES. 



The electrical resistance exhibited by trees is quite large, other- 

 wise considerable more injury might result when live wires carrying 

 strong currents are brought in contact with them. The resistance 

 offered by lo feet of the trunk of a maple and elm tree, 12 in. and 

 18 in. in diameter respectively, is as follows: 



TABLE SHOWING THE RESISTANCE OF DIFFERENT TISSUES OF THE 



MAPLE AND ELiM TREE. 



Maple. Elm. 



(Ohms). (Ohms). 



Outer bark, 192000 



Middle of inner bark (cortex), 29900 11300 



Cambium (vital layer), iSooo 10698 



Wood, yl in. in from cambium, 13S000 98700 



These figures which are the result of only one test taken during 

 the month of June show that trees possess considerable electrical 

 resistance. Such resistances as are shown in the table are capa- 

 ble of cutting down tolerably high currents to an insignificant 

 amount. As might be expected, the cambium or vital tissue and the 

 inner bark, containing the phloem, show the least resistances. The 

 resistance of the outer bark of the elm tree was reduced quite per- 

 ceptibly after turning a hose on it for four hours. The bark, how- 

 ever, in the elm is more differentiated than in the maple, and the 

 electrodes in the middle or inner bark test in the elm were pratically 

 in the layer known as the phloem. 



Experiments have shown that those layers containing large 

 amounts of the sugar compounds have the smallest resistance, and 

 since these layers which contain sugar are close to the cambium, one 

 would naturally expect on this account to find the smallest resist- 

 ance in them. These resistances were taken with a ^^'heatstone 

 Bridge. Others have been estimated from the voltage and current 

 passing through the tree. In all cases the electrodes or wires were 

 driven into the tree so as to penetrate the wood. Some of these are 

 as follows : 



A maple tree, 18 in. in diameter, gave a resistance of 20000 ohms 

 for 16 v< ft. of its trunk. The same tree gave iiooo ohms for 7 ft. 

 of the trunk, and 7000 ohms for one foot. 



A pear tree, 2 ft. 8 in. high, \]^ in. in diameter at the base, gave 

 a resistance of 290000 ohms when the current passed from the root 



