92 HABIT AND INTELLIGENCE. [cHAP. 



(and, doubtless, water also) that is decomposed by the 



green leaf is the sun's radiance that falls on it. As the 



actual energy of the electric current is, in the act of 



decomposing water, transformed into the potential energy 



due to the mutual affinity of the separated oxygen and 



hydrogen ; so the actual energy of the radiance that falls 



on a leaf is, in the act of decomposing the carbonic acid, 



transformed into the potential energy due to the mutual 



affinity of the separated oxygen and carbon. 



Contrast of Tlius we see that vegetables transform energy from the 



and ani- actual state of radiance to the potential state due to the 



mals. affinity of separated elements : and animals transform it 



back again into the actual state, either as heat, or as 



energy of muscular motion. 



In a word, vegetables take up. both matter and energy 



from the inorganic world, and the animals that feed on the 



vegetables give back the matter and the energy to the 



inorganic world again. 



Vegetable ^^ already stated, however,^ vegetables give out carbonic 



respira- a,cid, the formation of which is due to the slow oxidation 



of their substance ; and it is, no doubt, in consequence of 



this that, as ascertained by Dutrochet, their temperature 



while living is slightly higher than that of the surrounding 



air.2 This is a process of respiration, essentially similar to 



the respiration of animals. Eespiration consists in giving 



off the carbonic acid produced by the oxidation of the 



substance or the food of the organism : and oxidation is 



essentially combustion, and produces heat. Combustion 



is only rapid oxidation. 



. It is no new discovery, but a familiar truth, that a 



transfonn transformation of matter is, as we have seen in the 



1 P. 86. 



2 Carpenter's Comparative rhysiology, 3d edit. p. 846. It is from this 

 edition that I shall always quote. 



This fact shows that the energy which living vegetables transform, 

 exists previous to its transformation, not in the form of heat, but in that 

 of radiance. "Were heat transformed and destroyed, healthy green plants 

 would be sources of cold ; but we have seen that the reverse of this is true. 

 The coolness of vegetation as contrasted with the heat of bai'e earth or rock, 

 in warm weather, is due to the fact that living plants radiate heat abun- 

 dantly, and also produce cold by the evaporation of water from their leaves. 



