304 DISEASES OF TREES 



of the trees over considerable areas that have been affected by 

 lightning, a state of things that I have several times observed 

 both in young and old pine woods. 1 In such cases it was 

 remarkable that death, instead of affecting the whole area 

 simultaneously, spread centrifugally and radially from a given 

 point, and frequently continued to carry off the trees for five 

 years or more. An investigation of the trees showed that only 

 one or a few examples revealed traces of lightning, but that 

 between the crown and the collar of such trees, and many others 

 in their vicinity, the cortex was dead. In an old pine wood the 

 dead bark hung loose from the boles, while the crowns retained 

 perfectly green foliage. In a younger wood about thirty years 

 of age I found three stems showing traces of lightning along 

 the margin of the devastated area which had been steadily 

 extending for five years previously. The first of these had died 

 within the past year, the second still possessed a green crown 

 although its cortex and bast had died between the heights of 

 one and a half and eight feet, while the third, in spite of the 

 lightning having detached a broad strip of cortex, was perfectly 

 healthy in all parts. I confess that in face of these observations 

 I am unable to offer an explanation of the action of the 

 lightning. The fact that trees struck by lightning sometimes 

 remain alive for five years is to be explained in the same way 

 as the frequent survival for several decades of pines that have 

 been girdled. The water and plant-food move upwards in 

 the wood, and the crown, utilizing the products of metabolism, 

 remains healthy, and forms new organs. Death occurs only 

 when the exposed wood of the bole has gradually dried up 

 to such an extent that water is unable to pass upwards in 

 sufficient quantity. That a tree scored by lightning may 

 remain perfectly healthy, while a neighbouring tree not so marked 

 may die, may possibly be explained by supposing that in the 

 former case the electric current was confined within narrow 

 limits, whereas in the latter it was distributed over the whole 

 surface, or throughout the entire cortex, of the stem. 



1 R. Hartig, Zeitschrift fiir Forst- und Jagdwesen, 1876, pp. 330 et seq. 



