374 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



respiration, and Vrolik and de Vries, as well as other authors \ state that it 

 ceased when the plants were placed in nitrogen or hydrogen. The intra- 

 molecular respiration of aerobes sets free so little heat that special methods 

 are required to detect it 2 . Saussure 3 indeed observed that the spadix of an 

 aroid absorbs oxygen most rapidly when it is producing most heat, and 

 that the spathe which barely warms at all consumes but little oxygen. 

 Saussure 4 , Dutrochet, and Wiesner 5 have also shown 

 that in general the most active respiration occurs 

 during the period of most active heat-production, and 

 Bonnier's 6 quantitative estimations of the respiration 

 and heat-production of seedlings lead to the same 

 conclusion. An exact correspondence between the 

 curves showing the respiratory activity and the pro- 

 duction of heat is hardly to be expected, and the 

 divergences will be still greater between the respira- 

 tory curve and that showing the excess of tempera- 

 ture above the surrounding medium, since the amount 

 of excess is influenced by various factors. 



The table given on p. 375 was compiled by Garreau from 

 observations upon Arum iialicum. The spadix was enclosed 

 in a narrow graduated cylinder, and the thermometer laid 

 against it surrounded by muslin (d). The inner walls of 

 the bell-jar were smeared with potash, the rise of water in 

 the bell-jar giving the consumption of oxygen. During the 

 first six hours, with an air temperature of i6C., 470 c.c. of 

 oxygen were consumed, but only 300 during the following 

 eighteen hours, when the spadix was producing but little 

 heat. Kraus 7 has shown that during this period of active 



respiration the dry-weight may decrease by seventy-five per cent, in a few 



hours. 



FIG. 67. Garreau's appa- 

 ratus to show the relation 

 between the respiration and 

 the production of heat by 

 the spadix of Arum itali- 

 cum: (a) bell-jar, (b) ther- 

 mometer, (c) support for 

 spadix. 



1 Vrolik u. de Vries, Ann. d. sci. nat., 1839, 2<! s ^ r - T. XI, p. 79. A cessation of the produc- 

 tion of heat by the inflorescence of Colocasia odora was observed by Huber (Journal de physique, 

 1804, T. LIX, p. 284) after smearing it with oil, and similar observations were made by G. Kraus, 

 1. c., 1884, p. 60. 



2 J. Eriksson, Unters. a. d. bot. Inst. zu Tiibingen, 1881, Bd. I, p. 105; G. Kraus, I.e., 1884, 

 p. 61. 



3 Saussure, Ann. de chim.et de phys., 1822, T. xxi, p. 283. Dutrochet (I.e., 1840, p. 6) also 

 considered the heat to be produced by respiration. See also Garreau, Ann. d. sci. nat., 1851, 3* ser., 

 T. xvi, p. 250. 



4 Saussure, Memoires de Geneve, 1833, T. vi, pp. 251, 558. 



5 Wiesner, Versuchsstationen, 1872, Bd. xv, p. 155. 



6 Bonnier, Ann. d. sci. nat., 1893, 7 e se'r., T. xvin, p. 33. 



7 G. Kraus, Abhandl. der naturf. Ges. zu Halle, 1884, pp. 9, 67; 1. c., 1896, p. 271. See also 

 Knoch, 1. c., 1899, p. 52. 



