356 BOTANICAL GAZETTE [NOVEMBER 
Now, as far as temperature influence is concerned, the most 
fundamental generalization that physiology has yet been able to 
attain is that which may be termed the principle of temperature 
coefficients. This is primarily the application of the chemical 
principle of vaAN’t Horr and ARRHENIUS to vital phenomena. 
This principle states that, within limits, the velocity of most 
chemical réactions doubles or somewhat more than doubles for each 
rise in temperature of 10° C2 The principle fails to hold rigidly, 
even in the somewhat vague form in which it is stated, but it seems 
to express in an approximate way a fairly general truth in chemical 
phenomena. 
A considerable literature has developed about the application 
of this chemical principle in physiology. CLAusEN? determined 
the rate of evolution of carbon dioxide from seedlings and buds at 
several different temperatures and found that this rate somewhat 
more than doubled for each rise in temperature of 10°, up to an 
upper limit of about 40°C. CoHEN™ calculated from measure- 
ments of O. HERTWwiG" that the time consumed by developing frog’s 
eggs, for the completion of certain Sevelopaicires phases, about 
doubled for each fall in temperature of 10°. Miss MatTrHaEr” 
studied the influence of temperature on the evolution of carbon 
dioxide from leaves in darkness and also on the fixation of this gas 
by leaves in light, and showed that the vAN’t Horr—-ARRHENIUS 
principle holds also for these plant processes. A temperature 
coefficient of the same order of magnitude as is required by this 
principle was found, for a number of different physiological pro- 
*For one clear statement of this principle see van’T Horr, J. H., Lectures on 
theoretical and physical chemistry, translated by R. A. LEHFELDT. London. No 
date (author’s preface dated 1898). Part I. pp. 227 f, 
* CLAUSEN, H., Beitrige zur Kenntnis der Athmung der Gewichse und des 
pflanzlichen Stollen Landw. Jahrb. 19:893-930. 1890. 
* CouEN, E.; Lectures on physical Sep for physicians and biologists. 
Translated Be ities H. FisHer. New York. 
™ Hertwic, O., Uber den Einfluss der aioe auf die Entwicklung von Rana 
fusca und Rana esculenta. Arch. f. Mikroscop. Anat. und Entwicklungsgesch- 
51:319-381. 1898. 
™@ MATTHAEI, GABRIELLE L. C., E 
and respiration. III. On the effect of temperature on carbon ‘dioxide silt 
Phil. Trans. Roy, Soc. London B 197:47-105. 1904. 
1 +“ eimilation 


