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THE AMERICAN NATURALIST [Vol. XLIT 



Having now outlined the three fundamental principles 

 of reaction-velocity, the law of mass, and the catalytic 

 acceleration of reaction-velocity, we are in a position to 

 consider the broad phenomena of metabolism or chemical 

 change in the living organism from the point of view of 

 these principles of chemical mechanics. 



The Metabolism of the Plant considered as a Catalytic 

 Reaction. 



Plants of all grades of morphological complexity, from 

 bacteria to dicotyledons, have this in common, that 

 throughout their active life they are continually grow- 

 ing. Putting aside the qualitative distribution of growth 

 that determines the morphological form, as a stratum of 

 phenomena above the fundamental one that we are about 

 to discuss, we find that this growth consists in the assim- 

 ilation of dead food-constituents by the protoplasm with 

 a resulting increase in the living protoplasm accompanied 

 with the continual new formation of dead constituents, 

 gaseous C0 2 , liquid water, solid cellulose, and what not. 

 This continual flux of anabolism and katabolism is the 

 essential character of metabolism, but withal the proto- 

 plasm increases in amount by the excess of anabolism 

 over katabolism. 



Protoplasm has essentially the same chemical composi- 

 tion everywhere, and in the whole range of green plants 

 the same food-materials seem to be required ; the six ele- 

 ments of which proteids are built are obviously essential 

 in quantity as building material, but in addition small 

 amounts of Fe, Ca, K, Mg, Na, CI and Si are in some 

 other way equally essential. What part these secondary 

 elements play is still largely a matter of hypothesis. 



Regarding metabolism thus crudely as if it were merely 

 a congeries of slow chemical reactions, let us see how far it 

 conforms to the laws of chemical mechanics we have out- 

 lined. 



If the supply of any one of these essential elements 

 comes to an end, growth simply ceases and the plant 



