493 



new structure, produced as a result of the wound stimulus and in the form 

 of a circular zone of scantier and smaller cells. The plastic food material, 

 flowing toward these spots, cannot be longer used for cell increase, since the 

 need has been met. It will therefore be laid down in the form of reserve 

 substances. Hence the noticeable accumulation of starch directly about 

 the frost wound. 



As a positive result of the investigation, it should be cited that in coni- 

 fers a definite difference exists between artifically produced, eye-like wounds 

 due to lightning and to frost. In wounds due to lightning the dead bark 

 tissue dries rapidly and is then surrounded by a porous layer of cork which 

 forms a light colored outer ring. In frost wounds, the dead cells in the 

 interior of the bark parenchyma at first retain their former size. They are 

 enclosed by a circular zone of newly formed cells; these do not develop a 

 porous layer of cork, but rather form a slender parenchyma zone, with nar- 

 row lumina, which usually is richer in reserve substances than the normal 

 bark parenchyma. This zone, in a wound due to lightning, is formed next 

 to the cork zone. 



These statements are corroborated by von Tubeuf 's observation on the 

 differences between wounds due to lightning and to frost. In injuries 

 caused by lightning the ring of dead bark radiates into the healthy tissue in 

 constantly widening bands, while similar phenomena in the injuries due to 

 frost have not been observed in conifers up to the present. 



In regard to the theor\' of the action of lightning, the present obsena- 

 tions on the structure determine that the electric spark primarily produces 

 a dr>'ing of the tissue. 



Injuries to Trees in Cities and Towns. 

 With the increased use of electricity in cities, there is a serious menace 

 which must be mentioned. Stone's investigations^ show that the alter- 

 nating and the direct currents cause injuries by local burning. In dry 

 weather, this is less to be feared, but becomes essentially greater when the 

 bark is damp. The direct currents used by street car lines come under 

 especial consideration here. Besides killing this tissue, the weaker currents 

 also stimulate action. Both conditions should be closely examined. Dis- 

 charges into the earth during thunder storms are more frequent, according 

 to Stone's observations, than is usually supposed and they explain many 

 injuries in the trees, which often are also mistreated by the inconsiderate 

 cutting out of the branches in order to isolate the wires. 



Effect of Spray Lightning on Grapevines. 

 Among Calladon's" numerous observations on the action of lightning, 

 the statement is found that in a vineyard, the upper surface of the soil which 

 had been struck by lightning presented a regular, sharply defined circle, the 



1 stone, G. E., Injuries to Shade Trees from Electricity. Hatch EXper. Stat. 

 Massachusetts Agric. Coll. Bull. 91. Amherst, 1903. , 



2 Colladon, Daniel, Effects de la foudre sur les arbres et les plantes ligneuses. 

 Mem. de la soc. de phys. et d'histoire nat., de Geneve 1872, p. 548-53. 



