36 PHYSIOLOGY OF NUTRITION 



Great fluctuations in atmospheric pressure exert a marked influence upon 

 photosynthesis. 1 



The process of photosynthesis is dependent upon the amount of chlorophyll 

 present in the leaves. 2 The anatomical structure of these organs is also of 

 importance, the stomata playing a particularly pronounced role. Mangin 3 

 was able to show that when the stomatal pores are artificially plugged exchange 

 of gases is retarded. A privet leaf {Ligustnim vulgaris), the upper surface 

 of which was coated with petrolatum, decomposed 6.26 g. of carbon dioxide, 

 but only 1.92 g. was decomposed by a similar leaf coated on the under surface. 

 [Privet leaves have stomata only below, so that coating the upper surface 

 did not close the pores.] Stahl 4 arrived at the same result. Parts of the lower 

 surfaces of leaves that had been rendered free from starch were covered with a 

 mixture of one part of beeswax and three parts of cocoa butter, and the leaves 

 were then exposed to light; after being bleached with alcohol and then treated 

 with iodine, the part that had been covered was brown, while the remainder of 

 the leaf was dark blue (Fig. 18). Blackman's 5 results point to the same 

 conclusion. The size of the stomatal openings is also important. 6 



(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, dcg. C, -6 8.8 11.4 15 23.7 30.5 37.5 40.5 43-° 



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 ei 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. JQOS- 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 critical 

 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. 

 191 7.) 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. t,t,: 517-536. 1919.) corroborates the interpretation that 

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



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

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



2 Liubimenko, 1910. [See note 1, p. 35.] 



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

 879-881. 1887. 



4 Stahl, Ernst., Einige Versuche liber Transpiration und Assimilation. Bot. Zeitg. 52* : 1 17-146. 

 1894 



5 Blackman, F. Frost, Experimental researches on vegetable assimilation and respiration. — No. I. On 

 a new method for investigating the carbonic acid exchanges of plants. Phil, trans. Roy. Soc. London 

 B186' : 485-502. 1895. Idem, same title, No. 11. On the paths of gaseous exchange between aerial 



leaves and the atmosphere. Ibid. B: 186^ : 503-562. 1895. See Sect. IV. 



6 Kolkunov, V., Ueber die Abhangigkeit der Assimilation von der Grosse der Spaltbffnungen bei den 

 Gramineen. [Abstract in German, pp. 381-382; text in Russian.] Jour. Exp. Landw. 8: 369-382. 1907. 



