32 PHYSIOLOGY OF NUTRITION 



Sorbose is formed by the action of light upon a mixture of formaldehyde 

 and oxalic acid. 1 



Bonnier and Mangin, as has already been mentioned (see page 4), have 

 shown that if the interchange of gases accompanying the process of photosyn- 



CO 



thesis is determined independently of respiration, the ratio —pr- is found to be 



somewhat less than unity. From this we must suppose that 'substances other 

 than carbohydrates and less easily oxidized than these, are formed in the leaves 

 under the influence of sunlight. The supposition that proteins also arise in the 

 process of photosynthesis has been frequently advanced. This is supported 

 by the quantitative researches of Sapozhnikov, 2 in which he established the 

 fact that an increase in protein occurs parallel with the accumulation of carbo- 

 hydrates in light. Posternak 3 is of the opinion that oxymethyl-phosphoric 

 acid is also formed in leaves in the presence of light. 



According to Krasheninnikov 4 a definite relation holds between the amount 

 of carbon dioxide decomposed and the concomitant increase in dry weight, as is 

 evident from the following average values: for a square meter of leaf surface the 

 amount of carbon dioxide decomposed was 2286 cc. or 4.48 g., while the corre- 

 sponding increase in dry weight was 2.94 g. The increase in dry weight for 

 each weight unit of carbon dioxide decomposed was found to have the values 

 given below, for the different plant forms considered. 



Bamboo o . 60 



Cherry-laurel o . 60 



Sugar cane 0.67 



Linden o . 74 



Tobacco 0.68 



It is seen that this ratio appears to be fairly constant. The formation of a 

 carbohydrate with the composition C12H22O11 (like cane sugar) would give 

 this ratio a value of 0.64. 



Investigations upon the first products of photosynthesis agree with plant 

 analyses in showing that an assimilation of water occurs simultaneously with 

 that of carbon dioxide. In every green plant the formation of organic substance 

 in sunlight is accompanied by assimilation of carbon, hydrogen and oxygen. 

 The bulk of the dry weight of the plant is due to these three elements; this dry 

 weight is made up of about 45 per cent, carbon, 42 per cent, oxygen, 6.5 per cent, 

 hydrogen, 1.5 per cent, nitrogen, and 5 per cent, mineral constituents. Thus 

 plants obtain more than 90 per cent, of their dry weight from the carbon dioxide 

 of the air and the water of the soil. 



1 Inghilleri, Giuseppe, Photochemische Synthese der Kohlenhydrate. I. Mitteilung. Bildung von 

 Sorbose. Zeitsch. physiol. Chem. 71 : 105-109. 191 r. 



2 Saposchnikoff, W., Bildung und Wanderung der Kohlenhydrate in den Laubblattern. Ber. Deutsch. 

 Bot. Ges. 8: 233-242. 1890. Idem, Beitrag zur Kenntniss der Grenzen der Anhaufung von Kohlenhy- 

 draten in den Blattern. Ibid. 11: 391-393. 1893. Idem, Eiweissstoffe und Kohlenhydrate der griinen 

 Blatter als Assimilations-producte. 61 p. Tomsk. 1894. [Russian.] [Rev. by Rothert in: Bot. Centralbl. 

 63: 246-251. 1895-] 



3 Posternak, S., Contribution a l'etude chimique de 1 'assimilation chlorophyllienne. Sur le premier 

 produit d'organization de l'acide phosphorique dans les plantes a chlorophylle avec quelques remarques sur 

 le role physiologique de l'inosite. Rev. g£n. bot. 12 : 5-24, 65-73. 1900. 



4 Krascheninnikoff, Th., Ansammlung der Sonnenengergie in den Pflanzen. Moskow, 1901. [Russian.]* 



