ON OXYGEN. 7L 



gen without any oxygen, and that there is no 

 other source from which this supply can be 

 obtained. 



The hydrogen, therefore, necessary for the 

 formation of an organic compound, is supplied 

 to the plant by the decomposition of the water 

 absorbed by the roots. The process of assimi- 

 lation in its most simple form, consists in the 

 extraction of hydrogen from water, and carbon 

 from carbonic acid gas. The oxygen resulting 

 in both cases from such decomposition, being 

 either assimilated in the production of the acid 

 properties common to some plants, or rejected 

 to supply the necessary waste, or to re-form 

 water with the hydrogen emitted by- plants in 

 the process of decay. 



Oxygen, the other constituent of water, and 

 the vivifying principle of the atmosphere sur- 

 rounding the globe, is one of the most active 

 agents in nature-— it is the supporter of com- 

 bustion, the source of life to all living animals, 

 and acting as the prime agent in decomposing 

 other matters, and rendering it fit for other 

 processes, it enters into compounds with almost 

 every substance known, forming a class of sub- 

 stances called oxides, which from the variety 

 of forms under which they are found, and the 

 important new combinations they again enter 

 into with other substances, may fairly be reck- 

 oned as the most prolific in nature. 



The part this gas performs in the vegetable 

 economy is certainly subordinate to that per- 

 formed by carbon, nitrogen, and hydrogen ; its 



