393 



T. T. Baxinister and M. J. Vrooman 



value as far- red illumination increased. Maximum enhancements 

 were limited to a small region of very weak far-red (pg-^ 0.005 to 

 O.OIO) and blue illumination such that p-|_^0.05 to 0.15 . 



4000 »fl« cm'* ••€"■ 



Fig. 2. D(p , Vo) • Contours of D estimated from ex- 

 perimentally determined profiles. 



Fig. 2 shows that D depends on blue and far-red in qualita- 

 tively similar ways. As one illumination increases, the other 

 being constant, D rises sharply, then more gradually, then 

 becomes constant. At very high illumination, D apparently de- 

 creases. When both illuminations increased in a fixed ratio, 

 D continued to increase -- no msLximum being reached with the 

 illuminations employed. The highest values of D obtained were 

 '^O.OU and occurred with p-, = 0.2 to O.3 and pg = 0.1. 



PREDICTED FUNCTIONS 



Both the "spill-over" and "separately packaged pigment" 

 models assume that the rate of photosynthesis is limited to the 

 rate of the slower of two required photoreactions. (We assume 

 here that both photoreactions must proceed at the same rate as 

 the overall rate of photosynthesis.) In both models, absorbed 

 far-red quanta are presumed to be distributed in a fixed ratio 

 between far-red and short-wave photoreactions, distribution to 

 the far-red reaction predominating. Accordingly, the rate (pg) 

 of photosynthesis in far-red is limited to the rate of the short- 

 wave reaction . Then . . . 



