THE EVOLUTION OF HEAT BY A E ROBES 



375 



Presumably every influence acting on respiration will be reflected 

 in the production of heat, and it has in fact been observed that at lower 

 temperatures the excess of temperature over that of the surrounding air 

 decreases l . Bonnier also found that seedlings of Triticum produced per 

 kilogram per hour 2-1 kilogram-calories at 15-8 C, and 0-18 kilogram- 

 calorie at 5-7 C. It appears further that the production of heat, like the 

 respiratory activity, rises with increasing temperature until death ensues ; 

 and in fact thespadices of Aroids as well as masses of other plants may heat 

 themselves up to the fatal limit when heaped together and supplied with air ". 



No detailed research on the influence of the pressure of oxygen has 

 been carried out. Vrolik and de Vries, however, state that the temperature 

 of the inflorescence of Colocasia odora rises, and J. Schmitz that that of the 

 buds of Aesculus Jiippocastanwn does the same when the surrounding air 

 is replaced by oxygen 3 . This is probably the result of an increase in 

 the activity of respiration. 



Injuries increase the activity of respiration and also the production 

 of heat. Richards 4 was able to show this by means of a thermometer 

 in plants massed together, and in single organs by thermo-electric means. 

 The feverish rise of temperature in the potato spread not more than 20 mm. 

 from the injury and in a particular case amounted to 0-05 C. 15 mm. away- 

 and to o-2iC. immediately beneath the cut surface. An onion, on the other 

 hand, showed a rise of 0-28 C. beneath the cut surface and as much as 0-17 C. 

 at a distance of 45 mm. Injured onions when heaped together showed a 

 temperature higher by one or more degrees centigrade than uninjured ones. 



Richards inserted thermo-electric needles into sound potatoes, and when the 



1 Cf. Saussure, Me'moires de Geneve, 1833, T. vi, p. 251 ; J. Schmitz, Ueber die Eigenwarme d. 

 Pflanze, 187, p. 320. 



2 Saussure (I.e., 1822, p. 298) stated that the production of heat in the flower of Cticurbita 

 decreases above 15 to 2oC., while Vrolik and de Vries (1. c., 1836, p. 140, cf. also Caspary, Flora, 

 1856, p. 219) observed that above 30 C. the spadix of Colocasia produces less heat. Possibly this was 

 partly due to a rise in the rate of transpiration and partly to some indirect action on respiration. 



3 Vrolik and de Vries, 1. c., p. 77 ; J. Schmitz, 1. c., p. 51. 

 1 Richards, Annals of Botany, 1897, Vol. XI, p. 29. 



