372 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



development ', but the method is naturally not a particularly accurate one even for 

 comparative experiments. The amount of transpiration in saturated air forms a still 

 more unsatisfactory measure of the production of heat. 



SECTION 81. The Evolution of Heat by Aerobes. 



Lamarck was the first to observe the production of heat by the spadix 

 of Arum italicum 2 , and in the case of this plant as well as in that of Arum 

 maculatum a delicate thermometer may show a temperature 6 or ioC. 

 above the surrounding air when applied to the upper free sterile portion of 

 the spadix. A difference of I7-6C. has even been observed in the case 

 of Arum italicum^ and G. Kraus 3 obtained a rise of temperature of 27 C. 

 by grouping five spadices around a thermometer, and a rise of 35-9 C., 

 when the whole was covered by a cloth. In the last case the temperature 

 of the air was 15-4 C., and of the spadix 5i-3C., a temperature which 

 could hardly be sustained for any length of time without injury. A similar 

 rise of temperature was observed long ago by Huber 4 in the spadix of 

 Arum cordifolium (Colocasia odora\ and apparently all spadices are able 

 to raise their temperatures to a greater or less extent. 



Apparently this specially active production of heat is shown only during flower- 

 ing. In the case of Arum italicum and A. maculatum it begins during the. opening 

 of the spathe, increases for three or four hours, remains constant for the next one 

 or two hours, and then decreases to a minimum in the course of a few hours. In 

 other plants and aroids the rise of temperature is repeated at intervals, and the single 

 period of the two plants mentioned may begin at any time of the day, but usually 

 attains a maximum between 6 and 9 p.m., since the spathe commonly opens in the 

 afternoon or early evening. 



Dutrochet observed a rise of temperature in the sterile portion of 8-2oC., in the- 

 region of the male flowers of 4-9 C., and in the zone of female flowers of 1-4 C. 6 



1 Cf. Wilsing, Jahresb. d. Agrikulturchemie, 1884, p. 118. 



a Lamarck, Flore frar^aise, 1778, T. in, p. 538; Senebier, Physiol. vegetale, 1800, T. in, 

 p. 314 ; Huber, Journal de physique, 1804, T. LIX, p. 281 ; Goppert, Ueber Warmeentwickelung i. d. 

 lebenden Pflanzen, 1832, p. 25 ; Vrolik and de Vriese, Ann. d. sci. nat., 1836, 2 sen, T. v, p. 142 ; 

 1839, 2 e ser., T. xi, p. 77; van Beek and Bergsma, Observations thermo-e"lectriques sur l'e"levation de 

 la temper, des flours de Colocasia odora, 1838; Dutrochet, Ann. d. sci. nat., 1840, 2 e ser.,T. xnr, 

 p. 65; Brongniart, Nouv. Ann. du Musee d'histoire nat., 1843, T. Ill, p. 153; Garreau, Ann. de 

 sci. nat, 1851, 3" ser., T. xvi, p. 255 ; Romer, Mittheil. d. naturwiss. Vereins von Neu-Vorpommern 

 u. Riigen, 1870, p. 51 ; Hoppe, Nova Acta d. Leopold. Carol. Akad., 1879-80, Bd. XLI, p. 199; G. 

 Kraus, Ueber die BHithenwarme bei Arum italicum, Bd. 1, 1882 ; Bd. II, 1884 (reprint from Abhandl. 

 d. naturf. Ges. zu Halle, Bd. xvi) ; Ann. du Jard. bot. de Buitenzorg, 1896, T. xin, p. 217 ; Passerini, 

 Nuov. giornale bot. italiano, 1901, T. vin, p. 64. 



3 G. Kraus, 1. c., 1882, p. 12 ; 1884, P- 79- 



4 Huber, 1. c. Cf. G. Kraus, 1. c., 1882, p. 12. 



5 Kraus could detect no rise of temperature in the female flowers by means of a thermometer, 

 but Dutrochet succeeded in this by using a thermo-electric needle. Kraus denies the recurrence of 

 warming observed in Arum italicum by a few observers, and also shows that there is no evidence 

 to indicate whether the central or peripheral tissues produce most heat. 



