The Temperature-coefficient of Photosynthesis : 
A Reply to Criticism . 1 
BY 
A. MALINS SMITH, M.A. (Cantab.). 
With two Figures in the Text. 
Introduction. 
T HREE papers have recently appeared in the ‘Philippine Journal of 
Science \ two by Brown and Heise and one by Brown alone, adversely 
criticizing several current conceptions with regard to the rate of carbon 
assimilation in plants and the influence of the factors of temperature and 
light upon it. In the first (1917 «) Brown and Heise oppose the view that 
the temperature-relations of this process are such that it conforms to the 
van’t Hoff rule. In the second (1917#) they oppose the view that the 
magnitude of carbon assimilation is directly proportional to the intensity of 
illumination, holding that when the light is increased by equal increments 
the increments of photosynthesis form a rapidly declining series. In the 
third ( 1918 ), by Brown alone, some attack is made upon the evidence for the 
conception of limiting factors. 
The first of these papers is the most considerable, and is directed against 
the conclusions reached in a series of papers by Blackman and his co- 
workers, especially against the work of Matthaei ( 1904 ). The view of Brown 
and Heise is that carbon assimilation in plants is governed by low tempera- 
ture-coefficients, such as have been found to characterize photochemical 
reaction in vitro (1-04 to 1-42 for a rise of io° C.), instead of by coefficients 
of the magnitude of about 2-o, which are the rule for ‘ dark ’ reactions in 
vitro. 
Brown and Heise have not worked upon this subject themselves and 
provide no new data, but they endeavour to establish their position by 
selection, rejection, and correction of the published results of experimental 
workers in this field. The intensity of their conviction that these results 
must be wrong when they have no data of their own to start from would be 
rather puzzling were it not made evident that, having grasped the general- 
ization that all photochemical reactions have low temperature-coefficients, 
they have thereupon decided, quite a priori, that photosynthesis must really 
1 This paper forms Part XII of ‘ Experimental Researches upon Vegetable Assimilation and 
Respiration carried out in the Botany School, Cambridge. 
[Annals of Botany, Vol. XXXIII. No. CXXXII. October, 1919.] 
Pp 
