Light Conditions 73 
at point of contact, and drying out the limb above. With 
alternating currents the damage seems usually confined to 
this local destruction at or near the point of contact as a 
result of the heat created. With direct currents, in addi- 
tion to these local burnings, electric effects are sometimes 
noted at a distance, the escaping current girdling trees at 
the base, and killing the cambium without the characteristic 
burning at point of contact or at point of discharge. This 
appears to happen only when the positive current is not as 
usually carried by the feed-wire, but by the rail, and leak- 
age through imperfect rail-connection occurs. In an ob- 
served case the damage was done when the trees were four 
feet from the rail,“the moisture conditions of soil and bark 
being evidently most favorable for electric discharge. 
The only help is, of course, to string the wires outside of 
the tree line, or at least to prevent contact, keeping in mind 
that winds will sway the branches and that allowance 
must be made for this. 
No authentic cases of injury or death, due to the mere 
effect of the light of arc lamps, are on record. 
Light Conditions. Where trees are planted close to- 
gether, standing in groups or clumps, there is apt to be an 
uneven distribution of light, some trees or some parts of 
trees being deprived by their neighbors of a sufficiency in 
that respect. The light is necessary, as we have seen, for 
the leaf to perform its functions in assimilating food. Defi- 
ciency in this respect may show itself in efiolatzon, the leaves 
becoming small and elongated, and the leaf-stalks and 
branchlets thin and slender. Finally, when the shade 
becomes too dense, the shaded portions die. This very 
important observation is utilized by the forester in secur- 
ing branchless boles by the natural trimming that takes 
place in dense growths. 
4 
