370 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



In an experiment with germinating Barley carried out at i6C., each kilogram 

 weight produced per hour 3-72 kilogram-calories 1 . The respiratory quotient was 

 0-65, and the heat-production estimated from the liberation of carbon dioxide was 

 1.74 kg.-cal., from the absorption of oxygen 2-7 kg.-cal. For the ripening ears the 

 respiratory quotient was 1-05, the heat produced 0-24 kg.-cal., and the estimated 

 amount both from the consumption of oxygen and the evolution of carbon dioxide 

 0-3 kg.-cal. 



Both the respiratory activity and the production of heat attain a maximum 

 during germination, and subsequently gradually fall. An adult man produces per 

 kilogram per hour about 1-4 kg.-cal., but a puppy as much as 6-4 so that the 

 production of heat in seedling plants is quite comparable with that in animals. 



Few experimental researches on heat -production have been performed,, 

 but these suffice to show its dependence upon the respiratory activity, 

 and in fact the more readily followed changes in the heat-production 

 can be used to trace the wound-reaction in place of the respiratory changes. 

 Under constant conditions as regards the external loss of heat a change 

 of temperature must always indicate an alteration in the vital activity, involv- 

 ing an increase or decrease in the exothermic or endothermic metabolism. 



Methods. The warmth of the spadix of certain Aroids can either be felt or 

 shown by pressing a thermometer with a small bulb against the object. Germinat- 

 ing seeds, or flowers of Rhubarb or Chamomile, may be placed in a vessel as in 

 Fig. 65, through which a stream of air or of hydrogen saturated with moisture can 

 be drawn 2 . In the absence of oxygen the rise of temperature decreases to a 

 minimum 3 . For comparison a similar vessel should be used containing seeds killed 

 by steaming. If a large mass of germinating seeds is merely placed in a large 

 beaker and covered with a bell-jar, a rise of temperature of a few degrees may be 

 shown, and if the experiment is carried on in a large calorimeter, or if the whole 

 vessel is surrounded by cotton-wool, the temperature may be over ioC. higher than 

 that of the control. In some cases the rise is so high as to kill the seedlings, and 

 if in that case Aspergillus fumigatus or other thermophile organisms develop the 

 temperature may rise to over 60 C. 4 



To detect the slight warming of single organs thermo-electric methods were em- 

 ployed by van Beek and Bergsma, by Dutrochet, and by various subsequent authors 5 . 



of work. The heat of combustion of fats is greater than that of carbo-hydrates. Thus i gram of 

 glycerine produces 4,200 gram-calories; starch and cellulose, 4,100; cane-sugar, 4,000; lactose, 

 3,900; dextrose, 3,700; albumen, 5,000 to 6,000; fat, about 9,000 calories, when burnt into carbon 

 dioxide and water. Cf. Landolt and Bornstein, Physikalisch-chemische Tabellen.] 



1 Bonnier's results are given in terms of one hour. 



2 This method of heaping seedlings, &c., together to show the evolution of heat was first used 

 by Goppert, Ueber Warmeentwickelung in den lebenden Pflanzen, 1832, p. 10. 



3 See Eriksson, Unters. a. d. bot Inst. zu Tubingen, 1881, Bd. i, p. 105. 



4 Cohn, Schlesische Ges. fur vaterland. Cultur, 1888, p. 150; Ber. d. bot. Ges., 1893, General- 

 vers., p. 66. 



5 Van Beek und Bergsma, Observations thermo-electriques s. 1'elevation de la temperature des 

 fleurs de Colocasia, 1838; Dutrochet, Ann. d. sci. nat., 1839, 2 e s ^ r ' T.xn, p. 77; 1840, 2 e sen, 



