489 



flower pot, together with the plant, was charged. "If the other wire is 

 brought near the plant, a current of the positive and negative electricity is 

 seen which had been separated in the two conductors and then in the two 

 wires. The positive electricity flows out in the form of a light cluster, the 

 negative appears like Httle beads of light on the tips." Experiments with 

 spruces and pines proved that a considerable number of needle tips on a 

 plant, negatively charged, gave out the electricity in the form of beads of 

 light when approached by the positively charged wire. If, however, the 

 plant is charged positively, the electricity flows from the tips of the needles 

 without light^. 



It was observed in tender plants that if the positively charged wire is 

 held so high above the plant that there were no beads of light to be seen on 

 the edge of the blossoms and that no sparks jumped over, no injurie/s fol- 

 lowed. If this precaution was not observed, after a few minutes the petioles 

 and parts of the sprouts below them began to wilt. These appeared darkly 

 glassy as after frost or injury. It should be deduced from these experi- 

 ments, that quiet electrical discharges can not call forth a direct injury, but 

 that such an injury is felt at once if a spark discharge takes place. 



Differences Between Lightning and Frost Wounds in Conifers. 



As yet, in v. Tubeuf's published results of his experiments, there is 

 still lacking an illustration of the anatomic condition of the lightning 

 traces which manifest themselves as eye-like spots in the bark. (See Fig. 

 100.) Although in the works of Colladon and R. Hartig, mentioned at the 

 beginning of this section, we also find statements as to isolated, ring-like 

 traces of lightning, it still seems to me that further experiments must be 

 made to demonstrate whether such injuries could not be produced by frost. 

 My question has received added force since in deciduous trees I have ob- 

 served similar phenomena round about bast groups which, lying near the 

 eyes, had been injured by frost. 



In order to get reliable comparative material, I begged from v. Tubeuf 

 specimens of his spruce, artificially struck by lightning, and produced frost 

 wounds by exposing a healthy five year old pine (v. Tubeuf had also found 

 characteristic lightning wounds in pines and larches) in May for a night to 

 a temperature of y°C. below zero in a freezing cylinder. The tree, appar- 

 ently uninjured when taken from the freezing apparatus, was observed at 

 the end of the year. This delay was necessary in order to give it time to 

 heal over possible inner injuries as must also have taken place with the 

 lightning wounds. 



The pine showed inner injuries only in the bark on one side of the base 

 of the trunk ; indeed, partly in the form of isolated dead cells with brown 

 swollen contents in the middle of healthy parenchyma; partly in the form 



1 t)ber die Unterschiede in der Wirkung der positiven und negativen Elek- 

 trizitat. Compare Plowman, Electrotropism of roots. Americ. Journ. Sc. 1904. cit. 

 Bot. Centralbl. 1905, No. 40, p. 342. 



