THE TEMPERATURE COEFFICIENT OF PHOTOSYNTHESIS. 



By W. J. V. OSTERHOUT and A. R. C. HAAS. 



{From the Laboratory of Plant Physiology, Harvard University, Cambridge.) 



(Received for publication, October 28, 1918.) 



The temperature coeflEicient of photosynthesis presents an inter- 

 esting problem. On the one hand is the fact that hght reactions have 

 very low temperature coefficients; while on the other hand it appears 

 that the temperature coefficients of photosynthesis reported by various 

 investigators^ are as high as those of ordinary reactions. It should be 

 noted, however, that in a recent investigation van AmsteP found a 

 temperature coefficient of 1.26, but expresses doubt whether this 

 really represents the correct value for photosynthesis. 



The difficulties of determining temperature coefficients are great 

 in the case of land plants, for when leaves are exposed to sunlight their 

 temperature rapidly rises and it may fluctuate as much as 10° C. in 

 a half hour period. For this reason the writers have employed aquatic 

 plants which form thin layers, the temperature of which can be 

 sufficiently controlled. 



In the present investigation the plants were placed in tubes filled 

 with solution; these were immersed in a water bath the temperature 

 of which was kept constant within 1°C., which sufficed for the pur- 

 poses of the investigation. Thermometers placed in the tubes showed 

 that the temperature did not rise more than 1°C. above that of the 

 bath and that it did not fluctuate more than that of the bath itself. 

 The plant employed in these investigations forms such thin layers 



^ Cf. Matthaei, G. L. C, Phil. Tr. Roy. Soc., B, 1905, cxcvii, 47, and the 

 interpretation by Kanitz, A., in Temperatur und Lebensvorgange, 1915, p. 

 18. Also Blackman, F. F., and Matthaei, G. L. C., ibid., 1905, Ixxvi, 402. 

 Blackman, F. F., and Smith, A. M., ibid., 1911, Ixxxiii, 401. 



The results of these observers have been interpreted by Brown and Heise as 

 showing very low temperature coefilicients (Brown, W. H., and Heise, G. W., 

 Philippine J. Sc, C, 1917, xii, 1). 



^ van Amstel, J. E., Rec. trav. bot. neerlandais, 1917, xiii, 1. 



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