CHAPTER V 



THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



PART I 



THE PRODUCTION OF HEAT 



SECTION 80. General. 



PLANTS are poikilothermic organisms which assume approximately the 

 temperature of the surrounding medium owing to their relatively feeble 

 powers of heat-production and their excessive loss of heat by radiation and 

 transpiration. According to whether the former or latter preponderate, the 

 temperature will be slightly above or slightly below that of the surrounding 

 medium. 



Since the heat is produced by respiration, less will be formed by the 

 more feeble intramolecular respiration than by normal aerobic respiration. 

 In the case of anaerobes, however, the pronounced decompositions they excite 

 may be accompanied by a considerable liberation of chemical energy in the 

 form of heat. Many plants respire actively, and Fungi and Bacteria have 

 four to one hundred times the respiratory activity of mammals, so that 

 such organisms may produce relatively more heat even than birds. 

 Owing to their extensive surface area, and the usual presence of so much 

 dead tissue, most plants, even when transpiration is reduced to a minimum, 

 become hardly at all or only 0-3 C. warmer than the surrounding saturated 

 air. In dry air the transpiration usually keeps the temperature of the plant 

 slightly below that of the air. In fleshy actively transpiring bodies such as 

 the spadix of Aroids a pronounced rise of temperature is shown, whereas in 

 tubers, in the trunks of trees and in most thick organs respiration is relatively 

 feeble and the rise of temperature is usually less than in thinner but more 

 actively respiring organs. Most Fungi and Bacteria expose a large surface 

 to the air, and if grown under water the heat produced is naturally conveyed 

 away still more rapidly l . 



1 [The sporophores otAgaricus, Boietus, and Lycoperdon (Sclerodcrma) also form good material, 

 the thermometer being placed in a hole bored in the sporophore while young, and the whole as well 

 as the control thermometer being enclosed in cotton-wool. Similarly, vigorous broth-cultures of 

 bacteria, if aerated and then corked after the introduction of a thermometer, show a temperature 

 from o- 1 to 0-4 C. higher than that registered by a similar thermometer placed in a corresponding tube 

 containing sterile broth, both tubes being surrounded by cotton-wool. Since the specific heat of 

 water is high, this slight rise of temperature represents a considerable production of heat.] 



