12 MASS. EXPERIMENT STATION BULLETIN 156. 



that electricity sometimes becomes a primary and gas a secondary factor 

 in the death of trees. 



The phenomena associated with electrolysis are often complex and 

 difficult to do away with entirely, according to exjjert electricians, but 

 much of the trouble can be eliminated by proper bonding of the rails 

 of electric roads and the grounding of different systems. 



Electrolysis is more common in wet than in dry soils. Cases are on 

 record where severe electrolysis has taken place 700 or more feet from 

 the source of leakage. It more often becomes troublesome in cities 

 where numerous railways and public-service corporations of all kinds 

 make use of the streets. We have observed cases where plants have 

 been stimulated and their growth increased by escaping electricity in 

 the soil. 



Lightning. 

 The common effects of lightning strokes on trees are so well known 

 that it is not necessary to dAvell upon them here; but lightning does 

 not always strike a tree in the same way, and the peculiar effects some- 

 times produced are often interesting. Very powerful discharges of 

 lightning act somewhat like an avalanche, causmg a severe shattering 

 of the tissue, while less i^owerful discharges may remove a strip of 

 wood only a few inches wide and 1 or 2 inches 

 thick. Lightning often takes a spiral course, fol- 

 lowing the grain of the wood, which is sometimes 

 very iri'egular. Even when strips of wood 4 or 5 

 inches wide and 2 or 3 inches thick are removed, 

 in which case the electrical energy is enormous, 

 the i^ath of the discharge is shown only by a dark- 

 colored streak 2 or 3 millimeters wide. 



Sometimes trees are killed outright by lightning 

 without being shattered or disiDlaying any other 

 of the common effects. In such cases the discharge 



Fig. 11. — Cross-sec- -g apparently dispersed so as to cause no visible 

 tion of elm shown 



in Fig. 10; x= mechanical injury to the tree, but the girdling of 

 small dead area a large or Small area of the living zone or cam- 

 path of ii"-htnine- bium laj'er of the trunk would be sufiScient to 

 discharge. cause its death. However, in a very large number 



of instances neither death nor mechanical injury 

 of any importance takes place. Hundreds of trees are annually struck 

 by lightning that never show any effects except to those capable of in- 

 terpreting the small narrow ridges which later make their appearance 

 on the trunk. (See Fig. 10, Plate V.). In such cases the lightning dis- 

 charge follows the line of least resistance, — the cambium zone, — • 

 burning a small channel usually about 1 millimeter in diameter. The 



