78 STUDIES IN PLANT RESPIKATION AND PHOTOSYNTHESIS. 



such as were found by Warburg are not at all uncommon for phys- 

 iological processes.^ Becking^ has recently published a theoretical 

 discussion of the physical factors involved in the temperature 

 coefficients of vital phenomena. Osterhaut and Haas,^ on the basis 

 of determinations of the temperature coefficient of photosynthesis 

 of Ulva rigida, conclude that this process involves two reactions — 

 one a light reaction with a low temperature coefficient and an ordi- 

 nary chemical reaction with a high Qio. 



A detailed discussion of temperature coefficients can not be entered 

 upon here. Suffice it to say, however, that in a process such as 

 photosynthesis there enters such a large number of factors that 

 the question naturally arises whether the very small number of 

 really concordant results is not due to chance or more probably to 

 the choice of limited conditions to the exclusion of the broader 

 aspect of the question. The many factors and steps which con- 

 tribute to the complete process naturally produce a complicated 

 situation, and determinations of temperature coefficients must 

 represent the mean of a number of reactions. Thus, while the 

 rate of photosynthesis is reduced with a decrease in temperature, 

 the absorption of carbon dioxid at 25° is about half that at 5°.* 



Recent investigations in the field of photochemistry emphasize 

 the complex nature of these reactions, and it will require an enormous 

 amount of experimental data before the kinetics of the photosyn- 

 thetic process are made clear. Stokalasa's^ attempt to explain the 

 internal factor in photosynthesis on the basis of the radioactivity 

 of potassium, which is found in higher concentration near the chloro- 

 plasts, still requires much experimental evidence before it is beyond 

 the realm of the purely hypothetical. 



In the consideration of the relation between respiration and 

 photosynthesis it is primarily the mature leaf which must be studied. 

 The principal interest in photosynthesis centers about the leaf which 

 is producing carbohydrate material above its immediate needs. 

 For this reason also the behavior of germinating seeds or seedlings 

 which have available reserve food material is of rather secondary 

 importance in the study of photosynthesis. 



The problem of photosynthesis is essentially one of energy transfer. 

 Unfortunately, however, our knowledge of the energy relations in 

 photosynthesis, as well as of plant respiration, is most rudimentary. 

 The former is practically confined to the observations of Brown 



> Fawcett, H. S. University of California Publications in Agricultural Sciences, 4, No. 8, 217 



(1921). 

 2 Becking, L. B. Dissertation, University of Utrecht (1921). 



sQsTEBHAUT, W. J. V., and A. R. C. Haas. Jour. Gen. Physiol, 1, 295-298 (1919). 

 « WiLLSTAETTEK, R., and A. Stoll. I. c, p. 181. 

 sStokalasa, J. Biochem. Zeitschr., 108, 159-184 (1920). 



