422 



SCIENCE 



[N. S. Vol. XLVII. No. 1217 



In order to study the eflFects of tempera- 

 ture, light intensity, etc., it is not necessary 

 to know the amount of CO, abstracted; it is 

 sufBcient to compare the time required to pro- 

 duce the same change in the color of the indi- 

 cator under diiierent conditions. This gives 

 much more accurate results than comparison 

 of the amoTints of C0„ abstracted in equal 

 times. In case anything is added to the solu- 

 tion which changes its buffer value due allow- 

 ance must be made for this. 



It is evident that the method is accurate, 

 simple, rapid and convenient, permitting us 

 to measure minute amounts of photosynthesis 

 at frequent intervals. 



It may be added that aquatic plants are 

 greatly to be preferred to land plants for 

 quantitative studies of photosynthesis because 

 in the latter the temperature can not be satis- 

 factorily controlled while with the former the 



PH values of a series of mixtures (Palitzsch, S., 

 BiocJi. Zeit., 70: 333, 1915. Compt. rend. lab. 

 Carlslerg, 11: 199, 1916). Cf. MeClendon, J. F., 

 Gault, C. C, MulhoUand, S., Pub. 251 Carnegie 

 Inst., 1917, pp. 21-69. 



By plotting the c.o. of borax as ordinates and the 

 PH values as abscissae a curve is obtained from 

 which intermediate values can be obtained by 

 graphic interpolation. 



Prom the PH values found in sea water 0.21 

 must be subtracted on account of the ' ' salt error. ' ' 



fluctuations can be confined within one de- 

 gree, or less. 



Similar experiments were made with a va- 

 riety of fresh-water plants, including Spiro- 

 gyra, Hydrodictyon and Potamogeton. The 

 results were very satisfactory. The usual pro- 

 cedure was as follows: A gallon bottle was 

 filled with the water in which the plants were 

 growing, a little phenolphthalein was added 

 and a solution of sodium bicarbonate was then 

 added, drop by drop, ujitil a pink color was 

 produced.^ On pouring this into the tubes 

 used in the experiments the pink color was not 

 perceptible since the layer of liquid was not 

 sufficiently thick. 



When the algae were placed in these tubes 

 in sunlight a pink color appeared in a short 

 time. If the tubes were placed in the dark the 

 color disappeared as the result of respiration. 

 In many eases the algae lived for several days 

 in these tubes and made considerable growth, 

 showing that they were not injured. 



The method is well adapted to class work. 

 For ordinary laboratory demonstrations Pyrex 

 glass is not necessary since any good glass* 

 wiU answer. It will be found that some algse 

 (particularly blue-green and unicellular green 

 algae) will operate satisfactorily in diffused 

 daylight. It is important, however, that the 

 plants be in active condition. Aquatics are 

 apt to prove unsatisfactory in fall and winter 

 while in spring and summer the same species 

 may be very active. 



SUMMARY 



Minute amounts of photosynthesis can be 

 accurately measured by placing aquatic plants 

 in solutions containing bicarbonates, with a 

 little phenolphthalein, and observing changes 

 in the color of the indicator. 



The convenience, simplicity and rapidity 

 of the method make it as useful for class-room 

 demonstration as for quantitative investiga- 

 tions. W. J. V. OSTERHOUT, 



A. E. C. Haas 

 iiaboratoey of plant physiology, 

 Haevakd University 



8 This solution should be freshly made each day. 



9 Open bottles, test-tubes, beakers or tumblers 

 may be employed. 



