THE PRODUCTS OF PHOTOSYNTHESIS 197 



forces outside of the plant. To these belong the polarization of light, 

 the rotation of the earth and magnetic effects of the earth. The manner 

 in which these forces aft'ect chemical reactions, if at all, is not known. 

 Van't Hoff'*^ suggested that dextro- or levo-circularly polarized light 

 might affect the synthesis of compounds in nature. 



Cotton *2 reported that the two components of circularly polarized 

 light are differently absorbed by the two forms of colored tartrate salts. 

 Byk " then called attention to the fact that light is circularly polarized 

 by the surface of the sea, so that d-circularly polarized light predominates 

 and an asymmetric agent is thus present on the earth. In spite of 

 repeated and careful attempts to effect a direct asymmetric synthesis 

 by means of physical-asymmetric influences, these have not been suc- 

 cessful.** 



The resolution of an externally compensated substance into the 

 optically active components by crystallization has been a familiar phe- 

 nomenon since the classical researches of Pasteur and of Jungfleisch, 

 Kipping and Pope *^ substantiated the discovery of Jungfleisch that there 

 may be a preponderance of the d-salt in the crystallization of sodium 

 ammonium tartrate, though Erlenmeyer ^^ has shown that the preponder- 

 ance of the d or the 1 form is not a constant occurrence. It has naturally 

 suggested itself whether a partial crystallization of such a solution may 

 not lead to permanent asymmetry. This, under very restricted circum- 

 stances, seems to offer one possibility of the natural existence of an 

 asymmetric influence which, if present when the first living organism 

 started, might induce a perpetual asymmetry.*" 



3. A third possibility which suggests itself as a cause for the forma- 

 tion of asymmetric compounds in the plant is that there are asymmetric 

 influences within the leaf. There is considerable chemical evidence which 

 makes such a view theoretically possible. An asymmetric compound once 

 formed, the theoretical difficulties of producing other asymmetric com- 

 pounds disappear. Asymmetric compounds may give rise to other asym- 

 metric compounds in the course of chemical reactions and this original 

 asymmetry can in a sense be perpetuated. This, of course, does not 

 answer the question of the original asymmetric compound, and the re- 

 actions involving asymmetric compounds as reactants cannot in the 

 strictest sense be considered as asymmetric reactions. If, however, we 

 take the leaf as it now is, we know that it contains a variety of asymmetric 

 compounds and that this asymmetry can in a number of ways be imparted 

 to other compounds synthesized. 



"Van't Hoff, "Die Lagerung der Atome im Raiime," 1894, p. 29. Kimball, 

 "Pyreheliometer and Polarimeter Observations, Bull. Alt. Weather Observatory 2 

 Pt. 2. Nichols, Ph\s. Rev., 24, 497 (1908). 



"Cotton, Ann. Chim. Phy. (7), 8, 347 (1896). 



♦'Byk, Zeit. Physik. Ghent., 49, 641 (1904). 



"Bredig, Mangold and Williams, Zeit. angezv. Chem., 36, 456 (1923). 



*' Kipping and Pope, Jour. Chem. Soc, 73, 606 (1898). 



*■ Erlenmeyer, Biochem. Zeit., 52, 439 (1913). 



*' Fitzgerald, Nature, 58, 545 (1898). 



