495 



Fig. 102). The cambium formed first an irregular tissue, which gradually 

 passed over into normal wood (compare Fig. 99). 



From these statements we arrive at the conclusion that lightning (like 

 frost) also causes considerable injury by m'echanical action and, in fact, as 

 a result of sudden excessive differences in tension. The trunk reacts in a 

 different degree according to its age when injured by lightning. Where the 

 bark is not injured to its whole extent, the dead places are surrounded by a 

 cork layer. If the young wood is not entirely killed but only compressed 

 or torn, a parenchyma wood develops later, which slowly passes over into 

 normal wood, so that false annual rings can be produced. All phenomena 

 spread out gradually from the base of the trunk ; that is, they finally 

 disappear. 



It is a matter of course that micro-organisms infest all wounds due to 

 lightning and it is easily comprehensible that these cases have been described 

 as parasitic diseases. An example is offered by "Gelivure" of the grape 

 which has been described as bacteriosis, but, according to Ravaz and Bonnet, 

 is nothing less than a wound caused by lightning and' infested by bacteria-. 



Spray Lightning on Fields and Meadows. 



Steglich- observed one July a potato field which had been struck by 

 lightning. The lightning hit in two places and the plants became yellow 

 and died ; the stems seemed cracked open and perforated so that the walls 

 of the wound appesared torn. 



V. Seelhorst^ describes injuries to hects from lightning. In one case 

 the place struck formed a circle about 15 m. in diameter. In the middle of 

 the circle the heets were all killed. The leaves on the plants near the peri- 

 phery were wilted and discolored. Often individual specimens slightly in- 

 jured, stood between plants greatly injured. At times small cavities were 

 noticeable in the beet, especialh' in the head. In other cases, practical 

 workers speak of discoloration and weakening of the heads of the beets and 

 similar phenomena ; nevertheless, secondary parasitic influence may have 

 made itself felt here. Colladon* also makes a report of a beet field struck 

 by lightning. The leaves of injured plants were colored red, shrivelled or 

 torn in places and the edges partially dried. In one potato field the ma- 

 jority of the plants in the upthrown soil were found to be healthy; only in 

 one place did the base of the potato stem seem torn and burned. In the 

 place struck by lightning on a meadow, with a diameter of 6 m., the highest 

 thistle tips were killed, while the lower parts and the grass remained healthy, 

 although here and there the earth was found to have been torn up. 



To explain the circumstance that the condition of individuals hit on 

 similarly planted bits of land always varies, Rathay cites photographs of 



1 Ravaz, L. et Bonnet, A., Les effets de la foudre et la gelivure. Compt. rend. 

 1901, I, p. 805. 



2 Jahrb. d. D. Landw.-Ges. 1892. 



" V. Seelhorst, Riibenbeschadigung durch Blitz. D. Landw. Presse 1904, p. 515. 

 4 Loc. cit., p. 555. 



