LIGHTNING-STROKE ON TREES. 7 
that the beech was struck quite as frequently as any other 
species. At the same time he points out that in some places 
one sees certain species more frequently struck than others, for 
example, in the Riviera—the eucalyptus ; in Germany—the oak 
and pyramid poplar; and he explains this by the fact that these 
are the tallest trees in the neighbourhood. 
The numerous statistical records have no doubt been collected 
with the greatest possible care, but Hartig points out how 
unreliable they must be, as it is very easy to confound the 
amage done by lightning with that due to other causes and vzce 
versd. In fact, he states that he himself would formerly have 
recognised a very small percentage of those trees which as a 
result of his investigations he was able to prove had been struck 
by lightning. 
Lightning usually strikes the under part of the crown, the 
stem, or the larger branches. The crown remains healthy after 
‘the stroke for a time, but dies away subsequently when the stem 
has become dry. It is seldom that the top or stronger branches 
are knocked off by lightning. 
The root-system does not seem to be ever damaged by light- 
ning, or at most slight traces are left by the current, on some of 
the stronger side roots. 
Only dead or dry parts of the tree can be set on fire by 
lightning. 
Hartig states that he never observed in the whole of his 
investigations any cells ruptured or torn by the formation of 
steam as might happen if the heating by the electric current was 
very great. The cells collapse and shrink up, but are never torn. 
The whole phenomenon is a complex one, and notwithstanding 
Hartig’s brilliant work there yet remains a wide fie f 
investigation to be covered before we can satisfactorily explain 
all the effects of lightning on trees. 
