520 RESPIRATION AND FERMENTATION 



condition. In all other cases the cessation of respiration is an infallible 

 sign of death. (On post-mortem production of carbon dioxide, cf. Sect. 101.) 

 The cessation of oxygen-respiration ultimately causes death in aerobes, and 

 as a general rule is accompanied by a rapid or immediate cessation of growth, 

 plasma-streaming, and many other irritable movements. The existence of 

 any one of these activities forms one of the visible tokens of respiratory 

 activity, and the latter is no doubt an essential characteristic of every 

 living plasmatic organ, or particle of plasma, for in any isolated mass of 

 protoplasm streaming ceases on the removal of oxygen, and recommences 

 again in its presence l . 



Growth and streaming movements may continue in green cells exposed 

 to light in the absence of all external supply of oxygen. This is simply 

 because the processes of respiration and assimilation counterbalance one 

 another, the power of assimilating carbon dioxide possessed by the chloro- 

 plastids being more than sufficient to decompose the amount of this gas 

 produced by the whole of the rest of the protoplasm. The gaseous exchanges 

 connected with respiration become fully manifest in green plants at night or 

 when the chloroplastids have been rendered inactive 2 . Respiration is but 

 little influenced by light, whereas the assimilatory activity of a highly chloro- 

 phyllous organ may be twenty to forty times greater in bright light than 

 its respiratory activity, so that during the day the surrounding air becomes 

 poorer in carbon dioxide and correspondingly richer in oxygen. Hence 

 during the daytime a green leaf usually reassimilates the whole of the 

 carbon dioxide produced by respiration, although sometimes minute traces 

 may escape 3 . Even when the subaerial parts are assimilating most 

 actively, carbon dioxide may be excreted in abundance from the roots, 

 flowers, or fruits 4 , but in a confined space the whole of this will be 

 rcassimilated during the daytime, and as long as the plant remains living 

 this circulation continues without the dry weight undergoing any increase 

 or decrease. De Saussure 5 first correctly interpreted this phenomenon and 

 showed that death ensues sooner when the carbon dioxide evolved is 

 absorbed by means of potash. 



1 Pfcffer, Zur Kenntniss'd. FJasmahaut u. Vacuolen, 1890, p. 279. Cf. Sect. 9. [Provided the 

 protoplasm is strictly aerobic, for in certain cases intramolecular respiration may provide sufficient 

 energy to permit of the continuance of streaming for days or even weeks in the absence of free oxygen 

 (Nitella, &c.).] 



2 Cf. Sect. 58, and Bonnier et Mangin, Ann. d. sci. nat, 1886, vii. sen, T. in, p. 42. 



3 Garreau, Ann. d. sci. nat., 1850, iii. se'r., T. XV, p. 5; 1851, T. xvi, p. 271; Blackman, 

 Annals of Botany, 1895, Vol. ix, p. 164. [By means of the decolorization of a faintly alkaline 

 drop of phenolphthalein, it can be readily shown that traces of CO 2 escape from a green cell or 

 algal filament exposed to light in an atmosphere of pure hydrogen.] 



* Knop, Ann. d. Chem. u. Pharm., 1864, Bd. cxxix, p. 287; Corenwinder, Ann. d. sci. nat., 

 iS6S, v. ser., T. ix, p. 63 ; Deherain et Vesque, Compt. rend., 1877, T. LXXXIV, p. 959. Cf. Sect. 57. 



5 De Saussure, Rech. chim., 1804, pp. 60, 194. On the importance of auto-assimilation in 

 preserving the functional activity of chloroplastids, cf. Sect. 55. 



