IIG J. E. BRUGGER 



culturiiig conditions, previous history of the sample, etc. Algae cul- 

 tured in a glucose-rich medium showed a lowered initial section of the 

 curve. Algae grown in Knop's solution with ordinary air, as well as 

 those cultured in an NH4"*"-rich medium, showed steeper slopes than 

 the algae grown with COj-enriched air. No extended study was made 

 of the effect of the medium in which the algae were suspended during 

 the measurement. Work is being continued along these lines, however. 

 It was found most convenient to store the algae in the dark in carbon 

 dioxide-free air — in this way several experiments could be done on the 

 same batch of algae. For control, the first set of measurements was 

 repeated at the end. 



When one compares the curves obtained for 4% carbon dioxide 

 in air with those in unenriched air, he observes that (Fig. 2) the 

 principal difference is the earlier onset of saturation. When the car- 

 bon dioxide level is maintained at 4% but the oxygen concentration is 

 reduced (Fig. 1), one observes that the slope at high intensities be- 

 comes steeper and the break in the curve occurs progressively earlier. 

 At the same time the initial slope (below compensation) becomes 

 steeper. In the curve (Fig. 1) for 2% carbon dioxide in nitrogen 

 (oxygen less than 10~^ mm. Hg), there is essentially a merging of the 

 two breaks observed in the curve measured in 4% carbon dioxide in air. 

 The shape of these curves depends on the degree of anaerobiosis one 

 maintains. It was necessary to use very high flow rates for the CO2-N2 

 sweeping gas. When carbon dioxide is entirely absent but the nitrogen 

 contains 0.5% oxygen, the initial slope is only slightly different from 

 the slope at intermediate and higher intensities. The position of the 

 bend varied with the time the algae were exposed to the gas mixture. 

 In nitrogen containing no carbon dioxide or oxygen (less than 10 ~^ 

 mm. Hg), a linear dependence of fluorescence intensity on irradiation 

 is obtained. 



Low temperature increased the fluorescence and straightened the 

 curves. The results obtained under irradiation with green and yellow 

 light did not appear to differ significantly from those obtained with 

 blue Hght. In addition qualitatively similar results were obtained with 

 Scenedesmus ohliquus D3 and Ankistrodesmus braunii. Studies of the 

 effects of poisons have not been completed and will not be discussed 

 in this paper. Among those tried — phenylurethane, iodoacetate, 

 cyanide, carbon monoxide — the effects produced were understandable 

 within the framework of the interpretation which follows. In general, 



