22 BULLETIN 1379, U. S. DEPABTMENT OF AGElCULTUBE 



open with that under vegetation. The results indicated that under 

 trees and shrubs the potential gradient was greatly reduced. The 

 experiments of Grandeau were confirmed by Mascart (36). 



As opposed to the conclusion of Grandeau, the modern greenhouse 

 of steel construction constitutes in itself an approximation to a 

 Faraday cage about the plants growing within it, and yet the develop- 

 ment of the plants is surely not seriously impaired in consequence. 

 Likewise, Briggs and Shantz (10, 11), in their investigation of the 

 water requirements of plants, carried hundreds of pots of plants to 

 full maturity under a grounded metal framework, covered above and 

 on the sides with metal screen of J^-inch mesh, which must have 

 annulled the normal electrostatic field; yet the plants grown within 

 the inclosure were almost without exception superior in development 

 and luxuriance of foilage to those grown in similar pots outside. 



Lemstrom (82) conducted in Finland a long series of experiments 

 to determine, if possible, the influence of static electricity on plant 

 growth. The presence of strong electric charges in the atmosphere 

 of northern regions, as indicated by the northern lights, linked with 

 the astonishing development of vegetation in such regions, led him 

 to regard atmospheric electricity as an important factor in plant 

 growth. Garden vegetables, fruits, and small grains were subjected 

 to several different treatments in these investigations both in green- 

 houses and in open fields. Lemstrom summarized the results of his 

 experiments as follows: 



(1) The real increase due to electrical treatment has not yet been exactly 

 determined for the different plants, but we arc approaching its smallest value by 

 fixing it at 45 per cent. 



(2) The better and more scientifically a field is cultivated and manured, the 

 greater is the increase percentage. On poor soil it is so small as to be scarcely 

 perceptible. 



(3) Some vegetables can not endure the electric treatment if they are not 

 watered, but then they will give very high percentage increases. Among these 

 are peas, carrots, and cabbage. 



(4) Electric treatment when accompanied by hot sunshine is damaging to 

 most vegetables, probably to all; wherefore if favorable results are to be arrived 

 at the treatment must be interrupted in the middle of hot and sunny days. 



Experiments similar to those conducted in Finland were conducted 

 in England, Germany, and Sweden with like results. A detailed 

 description of all of these experiments may be found in "Electricity 

 in Agriculture and Horticulture/' by Lemstrom (32). 



Priestley (42, 43) reported on the experiments of Newman (37) 

 at Golden Valley Nurseries at Bitton. A small Wimshurst machine 

 was used, one terminal of which was grounded and the other connected 

 to wires suspended over outside plats and also to wires in seven glass- 

 houses. The wires were hung 16 inches above the tops of the plants 

 and were provided with discharge points hung at short intervals. 

 The machine was operated 9.3 hours a day for 108 days between 

 March 27 and July 20, the first half of the period in daytime and the 

 latter half at night. Control plats were provided in all cases similar 

 to the treated plats except without wires. The results recorded 

 are given in Table 22. 



