THEORETICAL CONSIDERATIONS 261 



This second step has been accomplished in the laboratory and 

 outside the organism by Meldola/*^ but the gap between CO2 and 

 formaldehyde was not bridged until Fenton ^ reduced the former to 

 the latter in one step, with the aid of metallic magnesium, without 

 the intervention of the formic acid stage. At about the same time 

 (January, 1908) Gibson*^ and his collaborators, by means of a feeble 

 electric discharge, succeeded in synthesizing the formaldehyde from 

 CO3 in the presence of water. The securing of this result forms 

 part of the experimental demonstration of Gibson's photoelectric 

 hypothesis of photosynthesis. This hypothesis, in brief, is, "that 

 the light rays absorbed by chlorophyll are transformed by it into 

 electric energy, and that this transformed energy effects the decom- 

 position of carbonic acid (H^COg) within the cell, with the concomitant 

 formation of an aldehyde and the evolution of oxygen. 



The following facts in confirmation of this hypothesis have been 

 demonstrated in Gibson's laboratory : (i) That formaldehyde is 

 present in all actively photosynthetic tissues ; (2) that the amount of 

 formaldehyde present in the leaf bears a definite relation to the in- 

 tensity of illumination ; (3) that formaldehyde may be synthesized 

 from CO2 in the presence of water by feeble electric discharge ; (4) 

 that electric discharges of sufficient intensity occur in photosynthetic 

 tissues when they are adequately illuminated ; (5) that the light rays 

 absorbed by chlorophyll are those specially concerned in the genera- 

 tion of the electric currents which Kunkle,^ Haacke,^ and others * 

 have demonstrated to exist in chlorophyll-bearing tissues. Gibson's 

 hypothesis varies from all others in regarding the electric currents 

 as due to the transformation of the energy of the light rays, and in 

 attributing the formation of the formaldehyde from COg and water 

 to the electric energy thus derived. 



Whether further experimentation shall confirm these results or 

 not, it is certain that several steps are involved in photosynthesis. f 

 Several possibilities are open, therefore, as to the way or ways in 

 which radium rays or any other stimulus may affect the process. 

 The rays may affect any one or all, or any combination of two or 

 more of these steps, or they may modify the power of the plastids to 

 produce the necessary chlorophyll, or to convert sugar into starch.^ 



* See citations Nos. 8, 49, 50, 51, 53-5S. 



t Kimpflin ^^'^ ( 190S) considers that there are two distinct acts in the assimilation 

 of carbon: i. The production of electricitj', which, bj ionizing the water will increase 

 the amount of hydrogen in the nascent state. 2. The reduction of COj bj that 



