48 1 



perfectly healthy trees have been set on fire^ ; rather most investigations show 

 that only trunks rotten at the core were set on fire. 



The individual condition of trees, as well as the intensity of the light- 

 ning, governs the extent of the injury. It is found that different varieties 

 of trees frequently show similar injuries and that certain kinds are especially 

 apt to be struck by lightning, while others rarely. 



It should be stated, first of all, in regard to the nature of the injuries 

 that in most cases the torn bark exposes the wood, but that with varieties 

 which are good conductors, and in young trees, lightning may strike, leaving 

 no visible injury. As a rule, lightning does not strike the tip of the pyra- 

 midal poplar, but further down on the trunk, so that most of the top remains 

 uninjured; the lightning then passes down the trunk in a splintered line 

 which is straight or only very slightly spiral. Wood and bark splinters are 

 thrown off; on the edges of this strip the bark is raised from the wood, the 

 edges themselves are not discolored. In the oak, however, the tip is often 

 struck and frequently large branches at the top are killed and broken off. 

 The splintered strip usually exhibits a strong spiral twisting- on the trunk, 

 its wood a more channel-like, hollowed lightning path, while, in the poplar, 

 sharply angled splinters indicate the course of the flash. Especially in oaks, 

 besides radial splits, the lightning also produces many tangential ones in the 

 direction of the annual ring. At any rate, the direction and form of the line 

 of splitting depend on the structure of the wood. The lightning follows the 

 path of best conduction ; hence the more the wood fibres are twisted, the 

 more the splinters are twisted. In Fig. 97 F. Buchenau and Nobbe" repro- 

 duced their observations on oak and show the spiral course of the line of 

 splitting especially well. Caspary's experiments on the effect of the sparks 

 from the discharge of a Leyden jar, loaded with 50 volts, confirmed the fact 

 discovered by Villari that the electrical spark can travel a much longer 

 distance longitudinally in the wood than transversely. Besides this, wood 

 offers a greater resistance to the spark in a tangential direction than in a 

 radial one. The relations of the extent and the place struck in longitudinal, 

 radial and tangential directions are, according to Caspary, in fresh linden 

 wood as 19: 2: I, in dry spruce wood, as 7 : 2 : i. The tissue was always 

 torn in the course of the spark and an extensive destruction of the cell 

 contents was perceived as a result of the heat. 



This result from the lightning could be demonstrated everv^where and 

 in the cases where no injur}' is outwardly recognizable, a narrowly limited, 

 easily overlooked point of entrance may never be lacking. Colladon* also 

 observed, for example, in a poplar and a spruce, especially characteristic 



1 Caspary, Mitteilungen liber vom Blitz g-etroffene Baume und Telegraphen- 

 stang-en. Schriften d. phys. okonom. Ges. zu Konigsberg 1871; cit. Bot. Z. 1873, 

 p. 410. Beyer, Blitzschlag. Verb. d. bot. V. d. Prov. Brandenb., 28 .Tan., 1876. 



- Buchenau, Abhandl. d. naturwiss. Ver. zu Bremen, Vol. VI. — Schriften d. 

 Leopold. Akad. d. Naturf., Vol. XXXIII, 1867. 



3 Dobner-Nobbe, Botanik f. Forstmanner. 4. ed. Berlin, P. Parey, 1882, p. 34. 



4 Colladon, Die Wirkung de.s Blitzes auf Baume; cit. Biedermanns Centbl. 

 1873, p. 153. Bot. Z. 1873, p. 686. 



