1904.] 



PUBLIC DOCl^MENT — Xo. 33. 



15 



has been used for these cxp(>rinieiits alone for some years. 

 Previous to usini;- the soil it was silted tliroug'h a sieve of |- 

 iiK'li mesh, and thorouahly mixed. After using the soil for 

 a few experiments, it was taken out, resitted and thoroughly 

 incorporated again ; and occasionally the boxes were shifted 

 about, that is, the normal or untreated boxes were substi- 

 tuted or ehanoed for those which had been treated. With a 



12 3 4 



Fig. 2. — LougitudiiKil Boction of l)oxe6 eniploj-ed in the electrical experiments, 

 showing ilitfereut methods of treatment. Size of boxes, fiS !)>■ 32 by 7 inches. 

 1, copper and zinc electrodes connected; 2, direct cuiTent with rheostat; 3, 

 atmospheric; 4, wire electroiles. C, copper electrodes; Z, zinc electrodes; 

 r, rlieostat; b, gravity cells; w, wires-; g, ground wire; p, (collecting pole, 47 

 feet high. 



few exceptions, copper or zinc plates were used for electrodes. 

 These were made the same size as the ends of the boxes, 

 and in a few exceptional cases two series of wires, strung on 

 a frame about three inches apart, were employed instead of 

 the plate electrodes. One of these frames of wires was 

 buried near the surface, the other being buried near the bot- 

 tom of the box. The current, therefore, had to pass from 

 one frame to the other in a vertical direction throujih the 

 soil. The strength of the currents was in most cases ob- 

 tained with the aid of a Weston milammeter, capable of read- 

 ing 2V of a milliampere, or about 27^0^0" ^^ ^1^ ampere. The 

 interrupted induced currents were estimated, and represent 

 only approximate determinations. 



In the radish experiment the seed was sown directly in 

 the treated boxes, whereas in the case of the lettuce the 

 plants were tmnsplanted into the treated boxes when of 

 suitable size to make good growth ; the latter plants, there- 

 fore, were not stimulated during the whole period of devel- 

 opment. Gravity cells were used in all cases except with 

 the interrupted induced current, in which case sal-ammoniac 

 cells were employed. 



