15 



voltage of 20000 to give one ampere current through this same tree 

 under similar conditions. In like manner the resistance would have 

 to be reduced from 20000 to 500 ohms, in this experiment, in order 

 to obtain one ampere current. In the experiment where the wires 

 were only one foot apart, the current was 70 milliamperes, and there 



was no evidence that a particle of 

 heat developed during dry weather. 

 The current that will kill a young 

 succulent plant will not kill a tree, 

 or cause it any injury, for example, 

 a current of even three milliam- 

 peres or less will kill a young plant, 

 whereas the same plant, when 

 more matured, would require a 

 much stronger current to kill it. 

 From this it will appear that a cur- 

 rent that will kill one plant in one 

 stage of development, will not in 

 another. There is therefore as 

 great a range in current required 

 to kill plants as there are stages 

 of development or individual- 

 peculiarities, and it is impossible 

 to state only in particular cases 

 and under certain conditions, 

 what a current of a definite 

 strength is capable of doing. 

 There are many factors which 

 enter into a problem of this 

 nature : such as the character of 

 the plant juices which the current 

 has to traverse, the area of cross 

 section of the conducting tissue, 

 and the conditions under which 

 the current is applied. An elec- 

 tric current may pass through a 

 wire of large diameter and cause 



Fig. 9. Slunuing the characteristic ^-^Q heating, whereas the same cur- 

 grooves on the trunk of an elm tree 

 caused by a feeble stroke of lightning. '(^^^'^ passed through a very small 



wire will produce intense heat. 



M.'-^' 



^S^le^-' iis.;-'^ 



