EFFECT OP ELECTRICITY ON PLANTS 



8S 



with Penicillium, in which case he obtained nega- 

 tive results. The writer is unable to find any indi- 

 cation of the potential employed in his experiments, 

 but from his results it would appear that he was 

 entirely out of range. If he had employed a poten- 

 tial of about fifty volts, different results would 

 undoubtedly have been obtained, inasmuch as such 

 has been the case with Monahan's experiments 

 with Mucor and Phycomyces, which are equally 

 delicate organisms. 



Recent efforts and results. 



The writer and some of his students have con- 

 ducted for many years an extensive series of ex- 

 periments dealing with the influence of current 

 electricity on plants. Only a part of the results of 

 these experiments has been published, and in giving 

 a resume of the subject of electricity and plant- 

 growth, the writer will draw deductions from his 

 various experiments representing data secured from 

 the use of over 50,000 plants. 



The experiments made by Kinney in 1896 showed 

 considerable acceleration in the germination of 

 seeds and growth of seedlings, and the idea that 

 weak currents of electricity act as a stimulus was 

 proved to be well founded. He experimented with 

 static electricity and also with direct and alternat- 

 ing currents, all of which gave decidedly positive 

 results. His experiments have been repeated by the 

 writer and assistants, with similar results. 



From experiments which the writer and his 

 assistants have conducted for many years in large 

 boxes charged with direct and alternating currents 

 and atmospheric electricity, it has b^en shown that 

 lettuce and radish crops are considerably accele- 

 rated In growth in all instances. The average per- 

 centage of gain in the electrically treated lettuce 

 plants in all experiments, as compared with the nor- 

 mal, or untreated plants, was 34.81. The average 

 percentage of gain of the electrically treated radish 

 plants over the normal, or untreated, ones was 

 37.34. The radish roots showed a gain of 17.26 

 per cent, while the tops or leaves showed 42.90 

 per cent gain. The strength of current employed 

 ranged from .05 to 1 milliampere. In these experi- 

 ments a large variety of plants has been employed, 

 with practically similar results. 



Bacteria are greatly affected by electricity ; they 

 increase in numbers at a very marked ratio when 

 stimulated. The process of fermentation by yeast 

 is also greatly accelerated by the application of 

 minute direct currents or by a single tiny spark 

 from a frictional machine. 



The range of currents acting favorably on 

 growth is limited and may be represented as rang- 

 ing from .005 to .55 milliamperes. Direct currents 

 are not so stimulating in all cases as alternating 

 currents, but static electricity stimulates very 

 appreciably. In the many thousand seeds which 

 have been used there is no evidence that electricity 

 awakens life in dormant seeds. It always acts as a 

 decided accelerator to germination and growth, but 

 the germinating capacity is in no way affected. 



Monahan has shown that charging air with static 

 electricity constitutes an important stimulus to 



B3 



CTx? 



seeds and plants. Germination and growth in such 

 instances are greatly accelerated. , He employed a 

 potential ranging from 50 to 175 volts, with most 

 excellent results. A too high potential or a too 

 strong current prevents growth, and if the current 

 is increased sufficiently it is easy to kill plants. 

 The maximum or death current is determined by 

 the nature of the plant, as well as the conditions 

 under which the plant is stimulated. On the other 

 hand, too weak currents do not produce perceptible 

 reactions. The optimum or best current the writer 

 found to be about .22 milliamperes. 



The connecting of copper and zinc electrodes 

 placed in soil constitutes a very effective method, as 

 well as one of the cheapest ways, of 

 stimulating crops by electricity. Strips 

 of copper and zinc one foot wide and four 

 to six feet long 



connected with _^,_^^^ _/'''7>"n~^ 



wires furnish a bat- C y^T/ ^^ ^ 

 tery when placed in ^^ ^^ 

 soil, which under 

 certain conditions 

 will generate an 

 optimum current. 

 The amount of cur- 

 rent which these 

 will produce de- 

 pends, of course, on 

 the size of the 

 metal plates em- 

 ployed, together 

 with the nature of 

 the soil and other 

 factors. A soil lack- 

 ing in organic mat- 

 ter and plant-food 

 will give less cur- 

 rent than a richer 

 soil. Plates six 



N 



inches by three feet pig. 49. to show the growth. 



"'' '^ of seedlings treated with' 



positive and negative 



currents of electricity. N, 

 normal untreated plant; 

 — , treated with negative 

 current: +, with positive current. 



in some soils would 

 give a current 

 ranging from .02 

 to 1 milliampere 

 when placed four 

 feet apart, whereas, if these same plates were put ' 

 in some of the highly manured Boston market-gar- 

 den soils, they would generate ten to twenty times 

 as much current in a tolerably dry soil, when placed 

 farther apart. The amount of resistance in well- 

 manured market-garden soils is extremely small, 

 and it has been estimated that if a large house 

 were provided with copper and zinc plates located 

 at either end and these were connected with wires, 

 a current could be generated sufficient to run a 

 small incandescent lamp. 



General observations. 



The extensive use of electricity in a commercial 

 way has introduced factors which have a bearing 

 on vegetation. The numerous high tension wires 

 used for street lighting purposes frequently come 

 into contact with beautiful shade trees and cause 

 mu?h afuT" Such injury, however, is mainly of a 



