2 DYNAMICS OF PHOTOSYNTHESIS 



man and Smith/ is not sufficiently accurate and convenient. The 

 difficulty was solved by developing a method which depends on the 

 fact that as the plants abstract carbon dioxide from the solution 

 it becomes more alkaline. 



In collaboration with Loeb^ one of the authors had observed that 

 certain marine algas when exposed to sunlight cause the sea water to 

 become more alkaline. Similar observations had been previously 

 made by various observers^ upon fresh water plants in solutions con- 

 taining bicarbonates. If bicarbonates are absent, little or no effect 

 is observed. The greater degree of alkalinity produced in the pres- 

 ence of bicarbonates is due to the fact that the plants abstract CO2 

 from bicarbonates. Thus in sea water (which normally contains car- 

 bonates and bicarbonates) the alkalinity produced in this way may 

 amount to more than pH = 9. 



In the case of marine plants it is not necessary to add bicarbonates, 

 since the sea water contains a sufficient amount. Such plants can 

 therefore be studied in their natural environment, which is a distinct 

 advantage over the methods hitherto employed, in which concentra- 

 tions of CO2 greatly in excess of the normal were maintained during 

 the experiments. 



In this connection it may be mentioned that some authors state 

 that the concentration of free CO2 is about the same in solutions con- 

 taining carbonates and bicarbonates as in the air above and that 

 plants in such solutions have no more CO2 at their disposal than land 

 plants. Aside from the fact that the amount of free COo in sea water 

 is not known, they seem to overlook the fact that when free CO2 

 is abstracted from a solution of carbonates and bicarbonates it is at 

 once partially replaced as the result of the dissociation of the carbon- 

 ates and bicarbonates, so that the plant receives at once what other- 

 wise must be more slowly supplied by diffusion. The carbonates and 

 bicarbonates constitute a reservoir of COo which may be depleted by 

 photosynthesis during the day and filled up during the night by 



^ Blackman, F. F., and Smith, A. M., Proc. Roy. Soc, Series B, 1911, Ixxxiii, 374. 



2 Loeb, J., The dynamics of living matter. New York, 1906, 98. Cf. Moore, B., 

 Prideaux,E. B. R., and Herdman, G. A., Proc. and Tr. Liverpool Biol. Soc, 1915, 

 xxix, 233. 



^ Czapek, F., Biochemie der Pflanzen, Jena, 2te Aufl., 1913, i, 519. 



