The Maximum Efficiency of Photosynthesis 113 



(ftj+jj — ^j) X kp 2 — (/z'j+zlJ — h'j) X k'p 2 



Oco 2 )j+JJ — Oco 2 )j = , ,r h , ,,, 



«O2/KC02 — k o<i\k co 2 



and if we write 



we obtain instead of [8] and [9] 



^02 = (*o 2 )j+jj — (*o 2 )j 

 3>co 2 = (^co 2 )j+jj — Oco 2 )j 

 H = Aj+zU — hj 

 H' = h' J+AJ — h'j 



H x & C o 2 — H'k'coz r 10 i 



2 &CO2/&O2 — k'cozlk'o-z 

 H x kp 2 — H' x k'p 2 



K02/^C0 2 « C 2 /* CO2 



wherej'02 and 3*002 are tne S as exchanges effected by the light increment \J. 



There can be little doubt that when the increment \J is added to a high overcompensating 

 intensity J the action of J continues. One might have been more doubtful for the case where \J 

 is added to dark cells (J = 0). But since the same efficiencies have been obtained for \J whether 

 J was quite large or zero, the validity of eqs. 10 and 11 is proved. 



8. The Light and Its Absorption 



A Steinheil glass 3-prism spectrograph, operated with a focal length of 195 mm. at//3.5 for the 

 collimator and a focal length of 710 mm. for the telescope was used as a monochromator. The slit 

 was illuminated with a 750-w. projection lamp. The image of the coiled filament at about 20° 

 to its plane was projected onto the slit with an auxiliary lens. A 1000-w. voltage regulator was used 

 to supply power to the lamp, which operated at constant current. 



The width of the entrance slit was about 2 mm., corresponding to about 20 m/i in the red 

 region. A slit was placed in the focal plane of the telescope and was adjusted to have a width of 

 about 30 m/( covering the region 630 — 660 rn.fi. A lens was placed behind this slit to throw, in 

 a weakly convergent beam, an image of the exit prism face on the bottom of the manometer vessel. 



The area of the beam at the vessel was about 3 cm. 2 and the energy flux was about 0.6 micro- 

 einsteins/min., or in terms of the actinometer 13.4 cu. mm. of Oo absorbed/min. This intensity 

 was decreased when desired by placing in the light beam just before the exit slit blackened wire 

 screens calibrated by the National Bureau of Standards. 



The beam of red light entered the manometer vessel in a vertical direction from below and was 

 completely absorbed in the cell Suspension. Its incident intensity, which therefore was also the 

 absorbed intensity, was measured actinometrically, and is denoted in the following experiments 

 as AJ. 



A second light source was a 100-w. incandescent lamp, kept constant by a 500-w. voltage 

 regulator. The lamp was mounted above the thermostat symmetrically to the two vessels and 

 could be moved vertically to produce the desired State of compensation or overcompensation in 

 the cells. The total absorbed intensity of this light is denoted in all experiments as J. It was not 

 measured,* because efficiencies were only calculated for the increment JJ and thus the action of 

 j was eliminated. 



Attention may be called to the different volumes of cells which absorbed the measured red light 

 from below and the unmeasured white light diffusely (mainly from above and the side, also some 

 from below due to reflection back from the tank bottom). When 300 cu. mm. of Chlorella, sus- 

 pended in 7 ml. of liquid, was placed in a rectangular vessel of 8 cm.' bottom area, as in most of our 

 efficiency determinations, then the red light \J was absorbed in a volume of about 3 0.1 = 0.3 cc. 

 On the other hand, the white light was absorbed in the greater part of the cell Suspension, because 

 the white light entered the cell Suspension through a greater surface and was on the average less 

 absorbed by the cells because of the shorter wavelengths also involved. 



In a discussion (Society of General Physiology, Woods Hole, June 22, 1949) the 

 question was raised as to whether the white light from the lamp above possibly did 



* One must be warned against measuring J actinometrically, J may contain a speccral region 

 that is absorbed by the Chlorophyll in the cells, but not by ethylchlorophyllide dissolved in pyridine. 

 Other spectral regions are not absorbed completely owing to the incident angles of the white light. 



8 Warburg, Zellphysiologie 



