6 BORTHWICK—ON THE EFFECT OF 
VII.). The tree had been evidently struck by lightning on 
several occasions with a lapse of a few years between each stroke. 
Along the fissures on the top and left-hand side (Plate VII.) the 
cambium had been killed in a narrow band and was in process 
of occlusion. The iarge split below was caused by subsequent 
shrinkage in drying, and shows well how the wood has split 
along a radial line of weakness, where on two separate occasions 
the cambium had been killed and the injury thereafter occluded. 
The concentric zones of lightning-tissue consists of parenchyma- 
cells only, on each side normal wood-elements occur. The cells 
of the medullary rays seem to undergo no change, but pass 
uninterrupted through the bands of lightning-parenchyma. 
There are three complete rings at fairly regular intervals passing 
from the centre outwards, the last complete ring is, however, in 
reality double, there being as it were a ring of normal woo 
bounded on each side by a parenchyma-band, and that is why 
this ring appears to be broader than the others. 
The tree was 61 years old when cut down in 1901. The last 
complete lightning-zone was formed fourteen years before felling, 
that is to say when the tree was in its forty-seventh year; the 
preceding one when the tree was in its forty-sixth year; the 
third one when the tree was in its thirtieth year ; the innermost 
zone when the tree was in its sixteenth year. Therefore the 
complete zones of lightning-tissue were formed respectively in 
1887, 1886, 1870, 1856. The first time the tree was struck in 
1856 the cambium seems to have escaped uninjured, but on 
the three subsequent occasions the cambium was killed in a 
very narrow strip always in the same radial line, as is shown 
by the occlusions. Between the bark and the zone formed in 
1887 there may be seen in the Figure what appears to be another 
complete ring, but it is in reality made up of several parts all of 
which were formed in 1898, or four years before the tree was 
cut down. In these later shocks the cambium has suffered 
in one or two places, as is evidenced by the partially-formed 
occlusions. 
As regards the liability of certain trees to lightning-stroke, 
Hartig states that no tree is immune, and as a result of his 
investigations he came to the conclusion that — will 
select one species quite as readily as another. He a 
