INJURIES DUE TO ATMOSPHERIC INFLUENCES 303 



a single tree, or they may be noticeable on a whole group of 

 trees. As regards the former case, we find that all trees are 

 subject to be struck by lightning, but that some are more liable 

 to suffer than others. Oaks and the Lombardy poplar would 

 appear to be struck most frequently, though the Scotch pine is 

 also very often affected ; whereas the beech enjoys comparative 

 immunity from such injury. Even in trees of the same species 

 the form of damage varies exceedingly. As a rule the injury is 

 confined to the separation from the wood of a strip of cortex 

 about an inch in breadth. This lightning score, which begins 

 in the crown, is frequently interrupted over considerable portions 

 of the stem. It may leave one side of the tree and appear on 

 another, again to return to the original side at a different level. 

 In stems with straight fibres it runs straight, but in trees 

 showing spiral growth it follows a similar course. At the 

 bottom of the tree it disappears between two roots close to the 

 surface of the ground ; or it runs for some distance along the 

 under side of a strong lateral root, and then suddenly disappears. 

 By this treatment the health of the tree is in no wise affected. 

 The narrow strip of wood is either wholly uninjured or else 

 reveals a small crack down the centre. Externally it shows but 

 little brownness, and in a few years it becomes entirely covered 

 over by a callus. 



In other cases trees (pines) that are struck by lightning 

 reveal externally the same form of injury, but in a few days 

 the entire cortex with the exception of that on the collar, 

 the roots, and the upper part of the crown dies and becomes 

 brown. Such trees generally wither up after an interval varying 

 from a few months to a year or so, although they may remain 

 alive for four or five years, to die at the end of that period. In 

 some cases the electric current barks the tree and leaves the 

 stem almost naked, or it splits the stem longitudinally into 

 several parts, dismembering it almost entirely, and scattering 

 large splinters to a distance of one hundred yards. In certain 

 cases all that is left in the ground is a short stump. 



It is only when the tree is perfectly dry, or possesses dry 

 branches or at least dry rotten wood, that the lightning sets it 

 on fire. Combustion does not follow in a fresh living tree. 



So far no explanation is forthcoming to account for the death 



