ASSIMILATION OF CARBON 35 



influence of temperature upon the velocity of the greening process has been 

 shown above. Photosynthesis, on the other hand, is only very slightly affected 

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

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

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



Temperature Amount oj CO2 Temperature Amount op CO2 



Deg. C. Decomposed Deg. C. Decomposed 



2-3 i.o 29.3 2.4 



7-5 1.7 330 2.4 



"•3 2.4 37.3 2.3 



iS-8 2.8 41.7 2.0 



20 . 6 2.6 46 . 6 1.3 



^S-° 2.9 



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 in temperature increases the rate of respiration to many times its original 

 value." 



Great fluctuations in atmospheric pressure exert a marked influence upon 

 photosynthesis. ^ 



The process of photosynthesis is dependent upon the amount of chlorophyll 

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

 importance, the stomata playing a particularly pronounced r61e. Mangin^ 



1 Kreusler, U., Beobachtungen fiber die KoHensaure-Aufnahme und -Ausgabe (Assimilation und 



Athmung) der Pflanzen. II. Mittheilung: Abh&ngigkeit vom Entwicklungszustand Einfluss der Tem- 



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

 atur; untere Grenzs der Wirkung. Ibid. 17: 161-175. 1888. Idem, Beobachtungen fiber 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.I 



2 Friedel, Jean, L'assimilation chlorophyllienne aux pressions inf^rieures h. la pression atmosphfirique. 

 Rev. gto. bot. 14: 337-355. 369-390. 1902. 



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



* Mangin, L., Sur le r61e des stomates dans I'entr^e ou la sortie des gaz. Compt. rend. Paris 105: 

 879-881. 1887. 



" 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 B 197: 47-105. 1905^ show 

 that the influence of temperature upon photosynthesis in leaves of Prunus 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 40.5 43.0 

 CO2 assimilated, g. 0.0002 0.0038 0.0048 0.0070 0.0102 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. I9°S- 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.|. 28: 628-636. 1908. — Ed. 



