OUTLINES OF THE PHYSIOLOGY OF NUTRITION 213 



It can only be performed by those parts of plants 

 which contain chlorophyll in their plastids. 



This process of the assimilation of carbon from 

 carbon dioxide may fairly be considered the most 

 important of all physiological phenomena, for on it 

 the whole existence of plants and animals is dependent. 

 Herbivorous animals eat plants, and are in their turn 

 eaten by carnivorous animals and by man. Our ow r n 

 life, and that of the whole animal kingdom, would 

 thus be absolutely impossible without the work done 

 by the chlorophyll-corpuscles of plants. 



We will now inquire what becomes of the carbon 

 after it is taken up by the plant. We know in a 

 general way that it is employed with other elements 

 to build up the protoplasm, starch, cellulose, and other 

 bodies of which a plant consists. Can we trace the 

 stages of the process ? Our knowledge here is still 

 very imperfect, but yet something has already been 

 made out. 



It is improbable that the carbon dioxide which is 

 absorbed is completely deoxydised. We know that 

 the simplest organic bodies found in plants contain at 

 least the elements of water, oxygen, and hydrogen in 

 addition to carbon. Now it is not likely that carbon 

 and water should enter into combination in the plant, 

 for both are chemically inactive bodies at ordinary 

 temperatures. If, however, water (H 2 0) as well as 

 carbon dioxide (C0 2 ) is decomposed, and the oxygen 

 given off is thus derived half from the carbon dioxide 

 and half from the water, the bodies remaining in the 

 plant will be carbon monoxide (CO) and nascent 



