Review of the early work.
Taking into consideration the results of the various experiments which are embodied in the foregoing résumé, there would appear, notwith standing the negative results, which, however, are considerably less than the positive ones, to be some reason for believing that electricity exerts an influence on plant growth. Many of the experi ments giving positive results were notably crude, especially the earlier ones, and even many of the later ones are not detailed enough to allow of any reliable conclusions being drawn. In the greater majority of cases too few plants were used, faulty methods were employed, the seeds were usually sown in earth where no accurate means of deter mining the relative acceleration of germination was possible. In the utter absence of measurements of current strength and the growth of plants, the results based on mere superficial comparisons were of little more value than guesswork. In some of the more recent experiments, however, compari sons have been made of the treated and untreated plants by weighing, and in some instances chemical analysis, a very uncertain method, was resorted to. On the other hand, it should be borne in mind that it is easy to repeat some individual experiment that gives a positive result, and by introducing some slight variation in the methods employed, or modifying the strength of current, results of a quite different nature may be secured.
The most severe criticisms that can be brought against the various experiments pertain to the lack of sufficient data concerning the current strength employed ; nor are there any data concerning the resistance or electrical potential from which the current strength might be calculated. The insuffi cient number of plants used and the lack of repe tition of various experiments under the same con ditions constitute serious objections. It would appear that individual variation as a factor was ignored in the majority of these experiments.
Since there is a limited range of current which accelerates growth, it is an easy matter to over step the range and obtain negative results. This would seem to be the case in the very carefully conducted experiments of Wollny. The same criti cism can be brought against Freda's experiments 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 s'imulus 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 been 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.