339 



C. S. French 



utilization of light in the other beam. However, this experiment 

 does not tell which beam makes the enhancing product. 



Experiments^"'' with light exposures of a few seconds duration 

 have settled this question, at least for Porphyridium . They 

 showed that more oxygen was produced by a green exposure if it was 

 preceded by a red exposure (Table 1), The converse effect: an 



TABLE 1. Peak Rates from 3-sec Light Exposures 

 in Porphyridium 



Green alone 



Green, 20 sec after red 



Red alone 



Red, 20 sec after green 



19.4 

 23.0 



17.1 

 14.0 



Enhancement 



Inhibition 



increase in yield in red light following green was not seen. 



In these experiments on Porphyridium I did not see any increase 

 during the dark time between the exposures as was found in both 

 Ankistrodesmus and in chloroplasts by Whittingham and Bishop' ■'-"^ . 

 In Porphyridium the amount of enhancement merely declined during 

 the dark time with a half-life of about 18 sec. 



Recently I looked for possible products of green light action 

 that might enhance photosynthesis by red light, but that might 

 have such a short survival time in the cells as to have escaped 

 detection with exposures of a few seconds and with corresponding 

 dark intervals of 20 seconds. In these experiments 10 ms paired 

 flashes of red and of green were given 50 ms apart but with long 

 dark times of 500 ms between successive exposures to the two 

 flashes. Even the long dark times were so short that the decay of 

 the red light product was insignificant. No difference was found 

 if the order of the flashes within each pair was reversed. Red 

 followed by green gave the same rate as did green followed by red. 

 Enhancement in Porphyridium therefore seems to be due to a red 

 light product that is used by green light. This finding implies 

 that the common method for calculation of enhancement as an in- 

 crease in photosynthesis in red light by added green should be re- 

 considered. At least in Porphyridium the utilization of a red 

 light product by green light given later shows that the enhance- 

 ment could perhaps better be expressed as an increase in the rate 

 of photosynthesis by green light when red is given before or dur- 

 ing the green exposure. 



