l6 PLANT RESPIRATION 



reaction of the living protoplasm to various stimuli. Hence 

 various kinds of studies of the action of external stimuli on 

 respiration have been carried out by many investigators. 

 We shall consider them briefly. The chief aim of modern 

 investigation is the solution of the problem of the real nature 

 of respiration; these questions are treated under the following 

 topics.'' 



The Influence of Temperature on Respiration. — Many 

 plants still respire at temperatures which are far below o°.^ 

 Thus the respiration of the leaves of conifers and Viscum 

 continues at —20°,^ although at a very slow rate. An increase 

 in temperature always effects an increase of the respiratory 

 energy in connection with which for the most part* the law of 

 van't Hoff^ prevails, that the temperature coefficient' is 2 — 3 



' Kreusler, U. Landwirtschaftl. Jahrb. 17: 161. 1888. 



2 Maximow, N. Bot. Jour. d. Xaturf.-Ges. in Petersburg. 1908. P. 23. 



'van't Hoflf. Vorlesungen. Vol. i, p. 229; Arrhenius, S. Z. f. physikal. Chem. 4: 226. 

 1889; Matthaei, G. L. C. Phil, trans, roy. soc. B. 197: 47. 1904; Blackman, F. F. and 

 Matthaei. Proc. Roy. Soc. London. B. 76: 402. 1905; Smith, A. M. Proc. Camb. Phil. 

 Soc. 14: 296. 1907; and others. 



'' A direct relationship between the rate of respiration and the percentage con- 

 tent of water in the moss, Hypnum triquetrum, has been reported by Mayer et 

 Plantefol, Ann. Physiol, et Phj'sicochim. Biol, i : 239-280. 1925. — Ed. 



'The agreement is closer for temperatures below 25°C.; cf. also Kuijper. 

 Extr. Trav-. Bot. Neerland, 7: 130. 1910. — Ed. 



'The term "temperature characteristic" has been proposed by Crozier (J. 

 Gen. Physiol. 7: 123. 1924-25 and other papers) as a name for the quantity 

 M, or E, in the Arrhenius-Marcelin-J. Rice equation for velocity of a chemical 

 reaction as controlled by temperature, this being of greater theoretical signifi- 

 cance than the Qio ratio. From the results of numerous experimental studies and 

 the analyses of existing records, Crozier has calculated ^l (the critical thermal 

 increment) of the Arrhenius equation 



for a number of vital processes including respiration. It appears that there are 

 two, probably three, well-defined "temperature characteristics" for respiration, 

 11,500, 16,200, and 8,000 (Crozier, W. J. J. Gen. Physiol. 7: 189-216. 

 1924-25). Each of these may be understood as a measure of the heat of activa- 

 tion for one molecule of the substance used in the respiratory process, or of the 

 respiratory catalyst. There is reason to think that the value 11,500 indicates 

 the existence of hydro.xyl ion catalysis as the "slow reaction" in such a catenary 

 series as A — ♦ B — + C, while 16,200 marks a slower aerobic respiration (possibly 

 catalysed by Fe). Hence the precise study of the influence of temperature on 

 respiration may lead to a more detailed knowledge of the chemical reactions 

 involved. — Ed. 



