CHAPTER X. 



ELECTRICAL DISCHARGES. 



Flashes of Lightning. 



In spite of numerous descriptions of destruction in the i)lant world, due 

 to lightning, we have not yet acquired an exact knowledge as to the way the 

 lightning acts. Just as in frost injuries, often similar to those produced l)y 

 lightning, we must distinguish mechanical and chemical action; in lightning 

 the mechanical action may be the more important one. Cohn^ compiled 41 

 cases where lightning had struck and an abundant bibliography. He states 

 that when lightning strikes, the main current of the electricity, after breaking 

 through the bark, passes down the tree through the cambial layer, which is 

 a good conductor. "The heat developed by the action at once vaporizes the 

 liquid contents in the cambial cells entirely or in part. The vapor, under 

 pressure, either bursts the bark, with the l)ast clinging to it in strips or 

 larger pieces. These broken ])ieces are fre(|uent]y thrown off to great dis- 

 tances. Besides this main current, a secondary current in the poorly con- 

 ducting wood will cause it to split where it is least firm, as a result of the 

 sudden dr}'ing due to the evaporation of the sap. Therefore, according to 

 Cohn's theory, neither the split wood nor the torn off strips of bark should 

 be considered as signs of the course of the lightning but only as indicating 

 the region of the least resistance. A\^ith Caspary, I would rather think that 

 the torn strips are the actual traces of the lightning. 



Cohn based his assumption that a sudden vigorous formation of vapor 

 due to evaporation in the tissue, struck by lightning, caused the explosive 

 scattering of the bark and wood splinters u]ion the following evidence. 

 First of all. dried splinters were actually ff)und. It is possible, however, to 

 observe this only rarely since, as a rule, the storm is accompanied by a 

 downpour of rain which immediately wets the dried chips. The fact that 

 trees may be set on fire by lightning, also favors the drying action. It should 

 be stated here, however, that as yet it has not been proved absolutely that 



1 Cohn. Ein interessanter Blitzschlag-. Vorh. d. Kais. Leop. Carol. Akad. d. 

 Naturf. Vol. XXVI, P. I. — tlher die Einwirkung des Blitzes auf Baume. Denk- 

 schrift d. Schles. Ges. f. vat. Kultur 1853, p. 267. 



