116 The Maximum Efficiency of Photosynthesis 



- is thus obtained by the measurement of three pressure changes. Their magni- 

 tudes were in the ränge of 25-50 mm. With every new experimental arrangement, 

 it must be checked, both for the cell Suspension and the actinometer, that the mano- 

 metric readings are independent of an increase in shaking rate. 



With regard to the outburst and inburst of CO- 2 , inferred during the last 10 years, 

 even if never demonstrated by published data in quantum yield experiments, it 

 may be emphasized that the quantum requirement per molecule of 0> obtained 

 by Eq. 14 is independent of all alleged fluctuations of C0 2 . When from the pressure 

 changes H and H' the gas exchange is computed by Eqs. 10 and 11, y 0l is ob- 

 tained independent of the C0 2 exchange and j>co 2 is obtained independent of the 

 2 exchange. Measurement of the 2 and C0 2 metabolism by the two-vessel me- 

 thod would be improperly understood if it were insisted, as upon occasion it has 

 been, that the 2 uptake after the interruption of Illumination could only be mea- 

 sured after 40 min. of dark, by which time the inburst of carbon dioxide would 

 supposedly be completed. On the contrary, for any period of time, during Illu- 

 mination as well as after illumination, the two-vessel method yields the 2 ex- 

 change independently of all C0 2 fluctuations, providing, of course, that physical 

 equilibration is adequately maintained. 



The described procedure for measurement of photosynthetic efficiency repre- 

 sents a very great simplification of the quantum requirement determination proce- 

 dures described in 1923 that were adopted in part but never in toto by later investi- 

 gators. The special differential manometer, inconvenient to handle, and the cathe- 

 tometer-microscope, are replaced by simple Haldane-Barcroft blood-gas mano- 

 meters and by direct Observation. The bolometer, with its manifold auxiliary 

 equipment, is replaced by the simplest of all such energy measuring instruments, 

 the manometric actinometer. Finally, especially when the monochromator is re- 

 placed by interference or other appropriate Alters, quantum requirements of photo- 

 synthesis may be performed as simple classroom experiments, and have been 20 . 



Experimental Details 



Our experimental equipment was set up by the middle of March: the Steinheil monochromator; 

 the thermostatted water-bath with Thermopane window, made by the American Instrument 

 Company (Silver Spring, Md.); the manometers and the rectangular vessels manufactured by E. 

 Machlett and Sons (New York City); and culturing arrangements for growing the strain of Chlorella 

 pyrenoidosa that was obtained through the courtesy of Dr. F. E. Allison of the Plant Industry 

 Station (Beltsville, Md.). In the very first experiment we obtained a quantum requirement of 3. 

 But it took us about two and a half months to find out the conditions under which high efficiencies 

 could be obtained in every experiment. In these two and a half months we observed quantum 

 requirements of 3 to 6, but also higher requirements, indeed as high as 20. We often observed 

 rapidly decreasing respirations and light actions in experiments with uncompensated respiration, 

 and could calculate by the equations of the two-vessel method a wide ränge of uncertain yields 

 because the necessary condition of these equations— identity of metabolism in the two vessels— was 

 not yet invariably fulfilled. Only gradually* did we come to clarify and identify the reasons for the 

 irregularities: the Sedimentation of the cells in the cultures, the not always adequate shaking of the 



* Zusatz 1961. Vergleiche hierzu die Arbeiten 27, 28 und 38, durch die das hier 

 diskutierte Problem vollständig gelöst worden ist (Notwendigkeit des blaugrünen 

 Lichts, Züchtung mit fluktuierender Intensität). 



