THE IMPORTANCE OF RESPIRATION 567 



and whether it is directly or only indirectly utilized in the performance of 

 the manifold synthetic processes of which the plant is capable. 



Energy is obtained in anaerobes in a similar manner to that liberated 

 by the explosion of gunpowder or dynamite, whereas aerobic respiration 

 may be compared with ordinary combustion in the presence of free oxygen 

 (Sect. 94). A production of heat accompanies both aerobic and anaerobic 

 respiration, and the chemical decompositions which accompany fermentative 

 activity usually induce a marked rise of temperature l . This heat- produc- 

 tion appears, however, to be simply the unavoidable accompaniment of 

 katabolism, for plants do not attempt to maintain a constant body-tempera- 

 ture, but allow the latter to rise and fall with that of the surrounding 

 medium. Hence they have necessarily acquired much greater resistant 

 powers to extremes of temperature than are possessed by warm-blooded 

 animals, whose body-temperature may vary only within comparatively 

 narrow limits. Under favourable conditions the respiratory activity and 

 production of heat is unit for unit more marked in certain plants than 

 it is in the higher animals, but owing to the relatively enormous radiating 

 surface area the temperature of even energetically respiring mould-fungi 

 hardly rises above that of the surrounding medium even when transpiration 

 is suppressed. 



Many marked manifestations of energy are not directly the result 

 of respiration ; this is the case for example with regard to the osmotic 

 energy by means of which comparatively enormous resistances may be 

 overcome, as when a root which grows into a crevice ultimatey bursts a 

 rock asunder. Such external actions may be measured, but it is impossible 

 to determine the actual value of the internal manifestations of energy, 

 and it is still uncertain whether the protoplasm directly utilizes the 

 chemical energy of decomposition, or whether the latter becomes available 

 in some indirect manner (PfefTer, 1. c., p. 177). Even although only a 

 fractional percentage of the total manifestations of energy directly result 

 from that liberated by protoplasmic respiration, and even though the latter 

 acts mainly in a preparatory or stimulatory manner or simply by providing 

 a supply of energy, it still remains the first essential for the maintenance 

 of vital activity. 



Only a portion, and probably only a small portion of the energy 

 liberated by respiration is converted into chemical or mechanical work, 

 for according to Rodewald 2 almost the whole of the energy actually 

 liberated appears in the form of heat. Even when the production of 



1 Cf. Pfeffer, Studien z. Energetik, 1892, p. 170. 



2 Rodewald, Jahrb. f. wiss. Bot, 1888, Bd. xix, p. 291, and 1887, Bd. xvm, p. 342. Cf. 

 Pfeffer, I.e., p. 201. Bouffard (Compt. rend., 1895, T. cxxi, p. 536) found that in the alcoholic 

 fermentation of 180 graj. sugar, 23-5 heat-calories were evolved instead of the theoretically-estimated 

 32-1. The deficiency may, however, be due to a variety of factors. 



