34 



EFFECT OF ELECTRICITY ON PLANTS 



local nature, — that is, trees are injured or burned 

 only at the point of contact of the wires with a 

 tree, and it can be positively stated that there 

 are no authentic cases of alternating current wires 

 killing large trees. The circumstances, however, 



might be different in 



the case of direct cur- 

 rent lighting wires, 

 providing sufficient 

 grounding occurred ; 

 nevertheless, so - called 

 direct current trolley 

 wires have been known 

 to kill large trees 

 where certain condi- 

 tions prevail. (Fig. 50.) 

 There is also some evi- 

 dence in support of the 

 prevailing opinion that 

 a certain leakage or 

 grounding from a trol- 

 ley system through a 

 tree may cause its death 

 in time without any 

 material burning tak- 

 ing place. In such 

 cases the tissues are 

 over - stimulated, as it 

 were, resulting in the 

 possible disintegration 

 of the protoplasm of 

 the cells. 



There is much evi- 

 dence in support of 

 the idea that electric- 

 ity plays an important r61e in nature. The air 

 and earth are constantly charged with it, and 

 vegetation, being in contact with both, is un- 

 doubtedly affected. Grandeau and others main- 

 tain that when plants are surrounded with wire 

 netting, they develop less in a given space of time 

 than plants grown under similar conditions as 

 regards light and other factors in a free atmos- 

 phere. The interpretation of this phenomenon is 

 that wire screens modify the atmospheric potential 

 to the detriment of the plant. Grandeau secured 

 similar results by growing plants under chestnut 

 trees, and he concluded that trees jnodify to a 

 large extent the atmospheric potential in their 

 immediate neighborhood. Electrical experiments 

 made for three years at the Massachusetts Agri- 

 cultural College Experiment Station show that the 

 electrical potential at corresponding heights in the 

 free atmosphere and in an elm tree are identical 

 during the season when no , foliage is present. 

 When, however, the foliage develops, the potential 

 drops materially in the air surrounding the tree 

 and remains in this condition until the leaves fall, 

 at which time the potential becomes identical 

 again. This is apparently a case of the foliage of 

 a tree absorbing atmospheric electricity or screen- 

 ing it in the some way as does a glass structure. It 

 may be interesting to no.te in this connection that 

 there is no atmospheric electricity in greenhouses, 

 but the effect of its absence on plants is not easily 



Fig. 50. Elm tree killed by a 

 direct current from an elec- 

 tric railroad system. 



discernible, since there are too many other factors 

 in greenhouses which modify the configuration of 

 plants. The electrical potential records secured 

 by the writer and his assistants under conifers, 

 such as the Norway spruce, proved the potential to 

 be similar most of the time to that of the earth 

 and not of the air, as secured under deciduous trees, 

 like the elm. Lemstrom was of the opinion that the 

 numerous small pointed leaves common to conifers 

 serve as points of discharge or accumulators of 

 electricity. This theory has some foundation, since 

 the apices of leaves of trees have been known to 

 discharge electricity, and the electric potential of 

 the air and earth may be more or less equalized by 

 vegetation. 



The phenomena underlying electrical stimulation 

 are still imperfectly understood. There are many 

 theories, however, in regard to its action. Nollet 

 and Jallabert thought that the accelerated growth 

 resulting from electrical stimulation was induced 

 by the augmentation in the movements of the sap, 

 and this view has been more recently held by 

 Lemstrom. Pichtner, Sohne and Tschinkel main- 

 tain that electricity renders soluble certain con- 

 stituents of the soil, as a result of which germina- 

 tion and growth are accelerated. On the other 

 hand, Jodro attaches double significance to the 

 action of soil currents, viz., a chemical and a 

 mechanical action. Chemically it renders those 

 constituents necessary for plant growth more 

 soluble ; mechanically it sets the particles of soil 

 into- a state of vibration which results in an in- 

 creased rate of 

 growth. It max ^^ 

 noted that both 

 the chemical and 

 mechanical theo- 

 ries fail to explain 

 the results of stim- 

 ulation of seeds not 

 sown in soil. 



It is well known 

 that feeble currents 

 accelerate the 

 movements of pro- 

 toplasm, and the 

 augmentative cir- 

 culation theory has 

 more to commend 

 it than any of the 

 others. Notwith- 

 standing the con- 

 siderable amount of 

 accelerated growth 

 manifesting itself 

 as a result of elec- 

 trical stimulation, 

 the time is not yet 

 opportune to apply 

 this force very 

 largely to the 

 growth of crops, 

 since the application of current electricity to crops 

 has not been sufficiently tested on a large scale ; 

 neither has it been demonstrated that electrical 



Fig. 51. To show tlie efCect of earth 

 discharge (lightning) through the 

 tree, causing splitting of the trunk 

 and limbs. 



