ELECTROCULTURE 15 



WATER REQUIREMENT 



An investigation of the effect of a high potential gradient on the 

 water requirement of cowpeas was undertaken in a plant house 

 during the winter of 1918. Eighteen large galvanizea-iron»can-. 

 each holding about 125 kilograms, were filled with well-mixed soil 

 and fitted with special covers to prevent evaporation. The cow- 

 peas were planted through holes in the covers, the openings being 

 sealed with wax. The pots were weighed at the beginning and at 

 the end of the experiment, and a record was kept of the water added 

 to each pot, from which the total quantity of water transpired by 

 the plants in each pot could be determined. In brief, the procedure 

 was that followed by Briggs and Shantz (10, 11) in their water- 

 requirement measurements. 



These pots were divided into three sets of six each. Set Xo. 1 

 was placed on an insulated stand, with each pot connected to the 

 positive pole of a static machine; set Xo. 2 w^as grounded and placed 

 under a positively charged iron-wire screen suspended about 2 feet 

 above the plants; and set Xo. 3 was used as a control and was protected 

 from the influence of the charged sets by a well-grounded wire screen. 

 The potential supplied by the static machine was above 50,000 volts. 



As soon as the treatment started trouble was experienced with 

 the set beneath the charged network, soot and dust (large ions) being 

 deposited on the leaves and stems of the plants, and in fact all over 

 the house. A coating would collect on the leaves over night during 

 the course of a 16-hour treatment. The plants were washed several 

 times, but they did not thrive, owing in part at least to the great 

 reduction in photosynthesis resulting from the coating on the leaves. 

 This set was finally discarded. 



The other two sets, however, grew well throughout the experi- 

 ment, although they were not so vigorous as plants grown out of 

 doors in the summer. The positions of the pots in a given set were 

 interchanged weekly, so as to provide average fight conditions for 

 each pot. 



The plants were cut May 2, after 54 days of treatment for 16 hours 

 each day (from 4 p. m. to 8 a. m.), and they were dried at 100° C. 

 and weighed. The water requirement of the plants in each pot 

 was computed by dividing the total weight of water transpired 

 by the dry weight of the crop. The mean water requirement for 

 each set of six pots with its probable error was as follows: For the 

 treated set, 449 — 4; for the control set, 429 ±5. A slightly higher 

 water requirement is thus shown for the treated set, the observed 

 increase being 4 ±1.2 per cent. If some of the water molecules 

 escaping through the stomata of the leaves carried a positive charge, 

 they would move away from the leaf more rapidly than under normal 

 conditions, owing to the strong electric field. This would be equiva- 

 lent to a virtual increase in the vapor pressure gradient near the 

 leaf and would tend to increase the evaporation rate. Although the 

 above suggestion is highly speculative, it would be of interest to 

 repeat the experiment, applying the electric charge during the 

 daylight hours when the transpiration rate is highest. 



SUMMARY OF EXPERIMENTS AT ARLINGTON EXPERIMENT FARM 



Electrocultural experiments extending over a period of eight years 

 have been conducted at the Arlington Experiment Farm. Rosslyn, 

 Va., for the purpose of determining whether a highly charged network 



