56 SILOS, ENSILAGE A1O> SILAGE. 



From the complexity and high potential energy of the 

 molecules of protoplasm, a reverse process at once begins 

 (destructive metabolism), and complex compounds are 

 resolved, step by step, into those that are relatively 

 simple, and starch, cellulose, and other plant constitu- 

 ents are formed, in the retrograde metamorphosis of the 

 protoplasm. 



This destructive metabolism is quite as essential to 

 the life and well-being of the plant as the parallel con- 

 structive process, and the two are simultaneously taking 

 place in the normal nutritive changes of every cell. 



The stored-up energy resulting from the cumulative 

 effects of constructive metabolism appears as heat in the 

 process of destructive metabolism, and when not util- 

 ized in work or dissipated by radiation, may be detected 

 by the thermometer, as in the ripening of fruits, the 

 malting of barley, and in the flowers of the Arum in the 

 experiments to which reference has been made. In the 

 normal life of plant cells there is, then, an expenditure 

 of energy in work, and a storing up of energy in com- 

 plex organic substances, which is immediately followed 

 by the breaking down of complex molecules, the libera- 

 tion of heat, and the elaboration of substances like 

 starch, cellulose, various nitrogenous bodies, and zy- 

 mases, which can be utilized by the plant, and inter- 

 vene between the complex protoplasm on the one hand, 

 and the final waste products on the other. 



It is important that we keep in mind the fact that the 

 heat resulting from the metabolism of plants and ani- 

 mals is evolved in accordance with the law of the con- 

 servation of energy which is as strictly applicable in the 

 organic kingdom of nature as in the inorganic. Plants 

 do not produce heat, in the ordinary acceptation of the 

 term, but it is liberated from the stored- up energy of the 

 more complex molecules when they are converted into 

 simpler compounds, as, for example, when starch is 



