468 



LIGHT AND LIFE 



possible separation in time of the mutually enhancing beams. The 

 theory of different products from specific pigments and the inter- 

 action of these products to give a greater rate when both are formed 

 together leads back to a biochemical search for the products them- 

 selves. If the investigators of the photochemical products of photo- 

 synthesis will stop using white light and will define their experimental 

 wavelengths with interference filters, I am sure we will see progress 

 in this field. 



It looks as though the effects we have been reviewing were super- 

 imposed on the main path of photosynthesis. A tentative scheme for 

 the accessory pigment function is illustrated in Fig. 18. In this pic- 

 ture most of the photosynthesis is presumed to be done by the major 

 forms of chlorophyll a, either by their own absorption or by energy 

 transfer through the accessory pigments. A second mechanism leads 

 to extra oxygen evolution by what is labelled the enhancement path- 

 way. To drive this enhancement mechanism, light must be absorbed 

 both by C.j695 and by an accessory pigment. Absorption by an ac- 

 cessory pigment produces a photochemical product called A, while 

 absorption by Ci,695 forms the photoproduct B. A and B then react 

 to give oxygen. 



The diagram also states that A and B spontaneously decompose to 

 inactive substances, P. The half lives of A and of B are not identical 

 but are both between 1 and 10 seconds. 



Qualitatively the diagram appears to provide for transients, en- 

 hancement, wavelength dependence of time course during and after 



Oi 



Fig. 18. A scheme to show the possible functional relations between several 

 forms of clilorophyll a and the accessory pigments of photosynthesis. 



