. Botanical gazette. Plants. I9I9] OSTERIIOUT—PHOTOSYNTHESIS AND RESPIRATION 61 The bubbling must be continued until the color becomes constant. When this is achieved we know that equilibrium has been estab- lished between the CO2 in the liquid and that in the chamber. In order to determine when the color of the indicator has become constant it is compared with a series of buffer solutions having the same concentration of in- dicator and contained in Pyrex tubes of the same size, as described in a previous article. The plant is now exposed to sun- light.' After exposure the gas is again bubble
. Botanical gazette. Plants. I9I9] OSTERIIOUT—PHOTOSYNTHESIS AND RESPIRATION 61 The bubbling must be continued until the color becomes constant. When this is achieved we know that equilibrium has been estab- lished between the CO2 in the liquid and that in the chamber. In order to determine when the color of the indicator has become constant it is compared with a series of buffer solutions having the same concentration of in- dicator and contained in Pyrex tubes of the same size, as described in a previous article. The plant is now exposed to sun- light.' After exposure the gas is again bubbled through the liquid. If the plant has taken CO2 from the air it will be evidenced by the change in the color of the indicator, which will show a greater degree of alka- linity than before. From the amount of change in alkalinity the change in tension of CO2 can be calculated; or the indicator may be cahbrated.^ For quahtative results the calcula- tion or calibration is not necessary. In the opinion of the writer, leaves of land plants are not suited to quantitative investigations on photo- synthesis, since on exposure to sun- light their temperature (and conse- quently the rate of photosynthesis) fluctuates greatly (as much as 10° C. in half an hour). This difficulty may be obviated by using suitable aquatics. For class demonstration it is not necessary to have a tube projecting through the lower stopper. The apparatus may be " The rise of temperature which occurs in sunlight tends to force gas out through the joints, which should therefore be made tight or sealed with water. * For methods see Henderson, L. J., apd Cohn, E. J., Proc. Nat. Acad. Sci. 2:618. 1916; McClendon, J. F., Gault, C. C, and , S., Publ. no. 251, Carnegie Inst. 1917. p. Fig. I.—.\pparatus for meas- urement of photosynthesis and respiration: p>lants are placed in the chamber; by means of bulb B gas in chamber is bubbled through indicator contained in tube .4; in- take of bulb i
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