57 o RESPIRATION AND FERMENTATION 



often the case, and seedlings of Helianthus annuus may perhaps continue 

 to grow for a short period without free oxygen, for Wieler 1 observed 

 distinct growth in an atmosphere containing at most 0-0003 per cent, 

 by volume of it. In such an atmosphere the oxygen-respiration is reduced 

 to a minimum or entirely suppressed, and intramolecular respiration only is 

 active. In the case of other seedlings growth ceases often even when the 

 oxygen percentage is not lower than 0-5 per cent. Correns found that 

 geotropic curvature is usually possible in the presence of 0-5 per cent, of 

 this gas, whereas heliotropic curvature is no longer produced in the case 

 of Sinapis seedlings in 6 per cent., and in that of sunflower seedlings in 

 i per cent., of oxygen. Similarly, streaming movements cease in some 

 cases only when the amount of this gas is reduced to a minimum, and in 

 others when it exists at a comparatively high partial-pressure, while it is 

 possible that in CJiara rotation may continue for a time in the complete 

 absence of free oxygen 2 . Since the cessation of such -movements may 

 also be induced by chloroform, high temperatures, &c., although respira- 

 tion persists or its activity increases, it is evident that the stoppage in the 

 absence of oxygen by no means shows that these functions are directly 

 dependent upon oxygen-respiration for the necessary supply of energy, and 

 this supposition is conclusively negatived when the functions are performed 

 for a short time under anaerobic conditions 3 . 



Normal respiration may continue for a limited period in the case of 

 certain pigment-bacteria by means of a store of occluded oxygen, but other 

 plants do not appear to possess any such "store 4 , as is shown by the rapid 

 cessation of various movements which are able to continue for days or 

 hours in the presence of a trace of oxygen, and by the immediate com- 

 mencement of intramolecular-respiration when all free external oxygen 

 is removed. It is possible that facultative anaerobes may continue to 

 respire normally for a time in the absence of free oxygen by means of 

 such a store, or even by utilizing the combined oxygen of highly oxidized 

 substances. Even in obligate acrobes single functions may not immediately 

 cease when aerobic respiration is no longer possible, and the fact that 

 certain phosphorescent bacteria continue to shine for a short time in the 

 absence of oxygen does not prove that these organisms possess a special 



1 Wieler, Unters. a. d. Bot. Inst. z. Tubingen, 1883, Bd. i, pp. 200, 223. 



* Cf. Lopriore, Jahrb. f. wiss. Bot., 1895, Bd. xxvm, p. 576; Ewart, Journ. of Linn. Soc., 1896, 

 Vol. xxxi, p. 420; Farmer, Annals of Botany, 1896, Vol. x, p. 288. [Kiihne states (Zeitschr. f. 

 Biol., 1898, Bd. xxxvi, p. i) that streaming may continue for fifty days in Niiella in darkness and 

 absence of oxygen, a fact which requires further confirmation, since a minute trace of oxygen may 

 suffice for the continuance of rotation (cf. Ewart, 1. c.).] 



3 Palladin (Ber. d. Bot. Ges., 1886, p. 322) supposes that respiration influences growth only by 

 producing osmotic substances, but growth is not solely dependent upon the osmotic pressure, and, 

 moreover, turgidity is at first unaltered when all free oxygen is removed. 



* Cf. Ewart, Journ. of Linn. Soc., 1897, Vol. xxxili, p. 123. 



