C THE CHEMISTRY OF THE FARM. 



The vegetable acids in a plant are probably formed by 

 oxidation ; most likely by the oxidation of some of the 

 carbo-hydrates. 



The fatty matter of a plant may be formed from carbo- 

 hydrates ; or possibly from the splitting up of albuminoids. 



We have just referred to oxidation as taking place in 

 the plant. This is always going on in the interior during 

 life, and as a result the plant is continually consuming a 

 small quaiitit}^ of oxygen, and giving out a small quantity 

 of carbonic acid, an operation precisely similar to animal 

 respiration. This action is not readily perceived during 

 the day-time, being hidden by the opposite action of the 

 chlorophyll cells, which absorb carbonic acid and evolve 

 oxygen. If a plant is placed in darkness the respiratory 

 action becomes manifest. The oxidation of matters already 

 formed is an important means for the production of new 

 bodies. 



The decomposition of carbonic acid by green plants 

 during daylight is of the utmost importance in maintain- 

 ing an atmosphere suitable for the respiration of animals. 

 An animal in breathing inspires atmospheric air ; it expires 

 air in which a part of the oxygen has been replaced by 

 carbonic acid; the result of animal life is thus to accu- 

 mulate carbonic acid in the atmosphere. Such accumula- 

 tion would be injurious to health, but is prevented by the 

 growth of plants. It has been calculated that an acre of 

 forest, producing annually 5755 lb. of dry matter, will 

 consume the carbonic acid produced by the respiration of 

 15.4 men. 



Besides carbonic acid, plants are apparently capable of 

 absorbing a small quantity of ammonia through their 

 leaves. The uncombined nitrogen of the atmosphere is 



