THE NATURE OF PHOTOSYNTHESIS 175 



Electricity : For more than a century the question of electro culture 

 and the influence of electric currents on the production of crops has, in 

 the hands of different investigators, been the subject of almost continuous 

 investigations. Few of these researches have been devoted to the more 

 immediate causes of the reported acceleratory action of electric currents 

 on the grovi^th of plants and the production of crops. There are a num- 

 ber of general theories, such as that of Lemstrom, that the electric cur- 

 rent "produces an augmentation of the energy with which the circula- 

 tion of the juices is going on." Also the acceleratory action has been 

 variously ascribed to the formation of nitric and nitrous acids, ammonia 

 and ozone. 



Relatively little work has been done on the effect of electric currents 

 on photosynthesis. Thouvenin has reported a decided acceleration of 

 the oxygen evolution by some aquatic plants in the light. Several Daniel's 

 cells in series were connected so that the two poles were at opposite ends 

 of a branch of Elodea. A current of 0.0005 to 0.001 ampere increased 

 the rate of oxygen emission taking place in the light. Plants in which 

 the photosynthesis was inhibited by chloroform were not affected by the 

 electric current. Pollacci reported an acceleration of starch formation 

 in land plants under the influence of direct current. His conclusion that 

 the electric current can replace radiant energy is of great interest, but 

 probably needs further confirmation. The direction of flow of the current 

 through the plant is apparently also of significance. The entire subject 

 is in need of thorough working over with a view of coordinating and ex- 

 tending the isolated observations and of establishing more accurately all 

 the chemical and electrical conditions involved.-^' 



Henrici ^" has made the interesting observation that the rate of 

 photosynthesis is influenced by the degree of ionization of the atmosphere. 

 In her experiments the air containing carbon dioxide was either discharged 

 or its conductivity increased by means of thorium oxide. The rate of 

 photosynthesis is greatly accelerated in an atmosphere of high conduc- 

 tivity. Under favorable conditions the rate of photosynthesis in ionized 

 air is 1.5-4 times that in discharged air. Thus, in an atmosphere of 

 high conductivity it is possible to obtain a rate of photosynthesis with a 

 light intensity which in unionized air produces no photosynthesis. How- 

 ever, no matter how great the conductivity, it is not possible to obtain 

 photosynthesis without light. The influence of the atmospheric ioniza- 

 tion is apparently closely associated with the carbon dioxide in the air. 

 Individual plants and different species exhibit a wide variation in their 

 reaction to ionized and unionized air and a great deal more experimental 



"' Lemstrom, "Electricity in Agriculture and Horticulture," London. Thouvenin, 

 Rev i/cii bat.. 8, 432 (1896). Pollacci. Atti. tst. Bnt. Paria (2), 13 (1907); Bot. 

 Cent.' 99, 544 (1905). Koltonski. Beih. Bot. Cent.. 23, 1, 204 (1908). Bo.se. 

 "Physiology of Photosynthesis," p. 72. Knv, Ber. bot. Ges.. 15, 398 (1897). Waller, 

 Attn. Bot., 39, 516 (1925). 



^Henrici, Arch. Sci. Phy. Nat. (5). 3. 276 (1921). Spoehr, Bot. Gas., 59, 

 366 (1915). 



