ASSIMILATION OF CARBON 35 



by temperature. According to the investigations of Kreusler, 1 the decomposi- 

 tion of carbon dioxide begins at temperatures almost as low as the freezing point 

 and continues up to 5o°C. His data are presented below. 



Tempera- Amount of Tempera- Amount of Tempera- Amount of 



tur e CO2 De- ture C0 2 De- ture CO2 De- 



Deg. C. composed Deg. C. composed Deg. C. composed 



2.3 1.0 20.6 2.6 37.3 2.3 



7.5 1.7 25.0 2.9 41.7 2.0 



11. 3 2.4 29.3 2.4 46.6 1.3 



15.8 2.8 33.0 2.4 



If the amount of carbon dioxide decomposed in a unit of time at 2.3 be repre- 

 sented by unity it is seen that this rate is not yet equal to 3 at 25 . Such a rise 

 of temperature increases the rate of respiration to many times its original value."' 



Great fluctuations in atmospheric pressure exert a marked influence upon 

 photosynthesis. 2 



The process of photosynthesis is dependent upon the amount of chlorophyll 

 present in the leaves. 3 The anatomical structure of these organs is also of 

 importance, the stomata playing a particularly pronounced role. Mangin 4 



1 Kreusler, U., Beobachtungen uber die Kohlensaure-Aufnahme und -Ausgabe (Assimilation und 

 Athmung) der Pflanzen. II. Mittheilung: Abhangigkeit vom Entwicklungszustand — Einfluss der Tem- 

 peratur. Landw. Jahrb. 16 : 711-755. 1887. [Idem, same title. III. Mittheilung: Einfluss der Tempera- 

 tur; untere Grenze der Wirkung. Ibid. 17: 161-175. 1888. Idem, Beobachtungen uber Assimilation 

 und Athmung der Pflanzen. IV. Mittheilung: Verhalten bei hoheren Temperaturen; Kohlensaure-ausschei- 

 dung seitens getodterer Exemplare; Kohlensaure Verbrauch, wenn Ober- und Unterseite der Blatter dem 

 Licht Zugewendet. Ibid. 19: 649-668. 1890.] 



2 Friedel, Jean, L'assimilation chlorophyllienne aux pressions inferieures a la pression atmospherique. 

 Rev. gen. bot. 14: 337-355, 369-390. 1902. 



s Liubimenko, 1910. [See note 2, p. 34.] 



4 Mangin, L., Sur le rdle des stomates dans l'entree ou la sortie des gaz. Compt. rend. Paris 105 : 

 879-881. 1887. 



w But Gabrielle Matthaei's very careful studies (Matthaei, Gabrielle L. C, Experimental 

 researches on vegetable assimilation and respiration. III. On the effect of temperature 

 on carbon dioxid assimilation. Phil, trans. Roy. Soc. London B197: 47-105. 1905) show- 

 that the influence of temperature upon photosynthesis in leaves of Primus laurocerasus 

 (cherry-laurel) is much more pronounced than is indicated by Kreusler's numbers. Her re- 

 sults are shown below, the amounts representing hourly rates per 50 sq. cm. of leaf. 

 Temperature, deg. C, -6 8.8 11.4 15 23^7 30.5 37.5 4Q-5 43-Q 

 CO-j assimilated, g. 0.0002 0.0038 0.0048 0.00700.0102 0.0157 0.0238 0.0149 0.0102 

 From these data it appears that the process in question about doubles for each increase in 

 temperature of io°C, thus agreeing with a large number of chemical reactions. (Van't Hoff, 

 J. H., Lectures on theoretical and physical chemistry, translated by R. A. Lehfeldt. London, 

 no date — author's preface dated 1898. Part I, p. 227 et seq.) See also: Blackman, F. F., 

 and Matthaei, G. L. C, Experimental researches on vegetable assimilation and respira- 

 tion. IV. A quantitative study of carbon-dioxide assimilation and leaf temperature in 

 natural illumination. Proc. Roy. Soc. London B76. 402-460. 1905. Blackman, F. F., 

 Optima and limiting factors. Ann. bot. 19: 281-295. *9°5- Idem, The metabolism of the 

 plant considered as a catalytic reaction. Presidential Address, Bot. Sect. British Assoc, 

 Dublin meeting, 1908. Also published in: Science, n.s. 28: 628-636. 1908. Two criticial 

 reviews of published data on photosynthesis may also be mentioned here; the first (Brown, 

 W. H., and Heise, G. W., The application of photochemical temperature coefficients to the 

 velocity of carbon dioxide assimilation. Philippine Jour. Sci. 12, C (botany): 1-25. 

 1917.) interprets the data as indicating that temperature has little effect on the rate of 

 the process, while the second (Smith, A. M., The temperature coefficient of photosynthesis : 

 a reply to criticism. Ann. bot. 33: 517-536. 1919.) corroborates the interpretation that 

 temperature has a pronounced effect on the rate. — Ed. 



