80 CHYMISTRY APPLIED TO AGRICULTURE. 



CHAPTER V. 



OP THE NOURISHMENT OP PLANTS. 



As soon as a plant begins to unfold its leaves, and to 

 fasten its roots in the earth, it is nourished by new 

 aliments, which it receives from the air and the soil by 

 which it is surrounded. 



The organs, which convey to the plant its new nourish- 

 ment, are principally the leaves and the roots. The leaves 

 absorb some of the gases contained in the air; and the 

 roots draw in, with the water containing them, the juices 

 and salts which are mixed with the soil ; and the gases 

 which are developed in it are imbibed by them through 

 the medium either of air or water. 



ARTICLE I. 



The Irifluence of Carbonic Acid upon Nutrition. 



Plants absorb carbonic acid from water and the air. 

 In the light they decompose it, and assimilate the carbon 

 and a part of the oxygen. 



A small portion of carbonic acid added to that existing 

 in the atmosphere is favorable to vegetation ; too large a 

 quantity is hurtful. 



The presence of this gas is indispensable to vegetation, 

 but the want of it is not equally great during all periods 

 of the growth of plants. A very young plant, of which 

 the leaves and roots have just begun to be developed, 

 languishes if watered with water containing the acid. 

 When it has acquired some strength and size, its growth 

 and vigor are increased by the operation. Sennebier has 

 observed, that young leaves decomposed, from an equal 

 volume of air during the same time, less carbonic acid 

 than leaves of full size. 



Vegetation can generally be accelerated by mixing with 

 the atmospheric air -^ or ^V ^^ carbonic acid gas ; but 

 this addition is not favorable unless the plants are ex- 

 posed to the sun. In the shade any addition whatever is 

 injurious. 



