322 THE FOOD OF PLANTS 



have shown that a larger volume of oxygen is produced than the volume 'of carbon 

 dioxide which is assimilated, but since in respiration the reverse takes place the result 

 is that the air of the receiver retains an approximately constant volume 1 . Thus, 

 according to Bonnier and Mangin, the total volume of the air is unaltered by assimi- 

 lating ivy leaves, although for every 100 cc. of carbon dioxide decomposed, 108 cc. 

 of oxygen are evolved. This is because the concomitant respiration produces 

 100 cc. of the former gas for every 86 cc. of oxygen absorbed (cf. Sect. 96). 



All researches have shown that oxygen is the sole gaseous product of carbon 

 dioxide assimilation, but any gases previously present in the plant may escape along 

 with it. This probably explains the increase in the percentage of nitrogen observed 

 by de Saussure in the surrounding air. The gas-bubbles evolved from water plants 

 during the assimilation of carbon dioxide contain less and less nitrogen if we 

 prevent the access of fresh supplies to the water, and hence to the plant also, 

 while that there is no evolution of carbon monoxide, or of gaseous hydrocarbons, 

 has been shown by Cloez and Corenwinder -. 



SECTION 55. Effect of the Accumulation of the Assimilatory 

 Products ( Carbohydrates). 



The assimilatory products are usually transferred by intermediate cells 

 to the neighbouring vascular bundles, and travel in the phloem, as well 

 as in the bundle sheaths and the parenchyma of the veins of the leaves, 

 by which paths carbohydrates, protcids, &c. may be carried considerable 

 distances 3 . Translocation of any substance is regulated by the amount 

 required for consumption or storage, and as soon as these cease the 

 assimilatory products accumulate in the conducting channels and in the 

 assimilating cells. As this occurs the assimilatory activity gradually 

 decreases and ultimately ceases (Sect. 93). 



Boussingault 4 incidentally observed that the power of assimilating 

 carbon dioxide gradually decreased in an actively assimilating branch 



1 Boussingault, Agron.,Chim. agric., &c., 1868, T. IV, p. 286; 1864, T. Ill, p. 378; Pfeffer, 

 Arb. d. lk>t. Inst. in \Viirzburg, 1871, Bd. I, p. 36; Godlewski, ibid., 1873, Bd. I, p. 343 ; Holle, Flora, 

 1877, p. 187 ; Bonnier et Mangin, Ann. d. sci. nat, 1886, vii. se"r.,T. Ill, p. I, where the methods by 

 which the respiration may be estimated are given. Jumelle, Rev. gen. d. Bot., 1892, T. IV, p. 61 

 (Lichens); Bastit, ibid., 1891, T. Ill, p. 521 (Mosses). On Crassulaceae, see Sect. 56. On the 

 ultimate changes produced as growlh continues, see Th. Schloesing, Compt. rend., 1893, T. cxvn, 



P- 756. 



2 Saussure, Rech. chim., 1804^.42; Cloez et Gratiolet, Ann. d. chim. et d. phys., 1851, iii. seV., 

 T. xxxn, p. 57. See also Boussingault, Agron., Chim. agric., &c., 1864, T. ill, p. 271 ; Cloez, 

 Ann. d. sci. nat., 1863, iv. se"r., T. XX, p. 180; Corenwinder, Compt. rend., 1865, T. LX, p. 120. 



3 Schimper, Bot. Zeitung, 1885, p 756 ; A. Fischer, Jahrb. f. wiss. Bot., 1891, Bd. XXII, p. 79 ; 

 Haberlandt, Physiol. Anat., 1884, p. 184, and Ber. d. Bot. Ges., 1886, p. 206. On the translocating 

 substances, see Brown and Morris, Journ. of Chem. Soc., 1893, p. 671. Cf. Chap. x. 



* Boussingault, Agron., Chim. agric., &c., 1868, T. IV, p. 312 ; Saposchnikoff, Ber. d. Bot. Ges., 

 1890, p. 238 ; 1891, p. 298 ; 1893, p. 391 ; Bot. Centralbl., 1895, Bd. LXIII, p. 246 ; Ewart, Jouru. 

 of Linn. Soc., 1896, Vol. xxxi, p. 429. On the slow disappearance of starch in separated leaves, 

 ef. Sachs, Arb. d. Bot. Inst. in Wiirzburg, 1884, Bd. Ill, p. 1 1 ; Saposchnikoff, I.e., 1890, p. 235. 

 On the influence of ringing upon translocation, see Cuboni, Bot. Centralbl., 1885, Bd. XX II, p. 48. 



