485 



characteristic form of the lightning- tissue in young wood would remove all 

 doubts. Such a picture of repeated and healed injuries, due to lightning, is 

 shown in Fig. 98. A similar constitution of the trunk could also indicate 

 frost wounds, only here the protruding frost cracks are lacking. Otherwise, 

 however, the anatomical changes in the tissue which set in in the sap wood 

 during the healing of the wounds due to lightning also exhibit a very great 

 similarity to that formation of parenchyma wood which usually follows 

 a frost injury. Since we will later consider the latter more closely, we will 

 give here, only for the sake of later comparison, R. Hartig's picture which 

 V. Tubeuf has recently reproduced^ We see in the lowest, thick-walled 



Fig. 99. Cross-section through an annual ring of a spruce in the year it was struck 



|jy lightning. The crumbled cell layer shows the effect of the lightning. 



(After V. Tubeuf.) 



tracheid layer (Fig. 99) the end of the previous annual ring. The new 

 annual ring has begun with the formation of thin-walled elements and was 

 struck by lightning when the loth to 12th summer tracheids had been 

 formed. The action of the lightning consists in the fact that the latest wood 

 elements have been displaced, slantingly pressed together, as if by a tan- 

 gential pulling, and in part killed, while the cell layers, remaining capable of 

 life, have developed into parenchyma wood and then gradually passed over 

 again into small celled normal wood. 



Healed wounds due to frost exhibit the same processes ; only, as a rule, 

 the abnormal layer of parenchyma wood is found nearer the old annual ring. 



1 V. Tubeuf, tTl)er sogenannte Blitzlocher im Walde. Naturw. Zeitschr. f. Land- 

 u. Fortswirtsch. 1906, p. 349. 



