278 INORGANIC MATTER. 



the tree which produced it, the soft pulpy matter of 

 the fruit soon decomposes, and by the time that the 

 seed begins to germinate, the fruit is wholly converted 

 into humus; hence the roots of the young plant are 

 placed in a soil rich in carbonic acid, as soon as it is 

 possible for them to absorb it. 



730. During the w^hole existence of a plant, from 

 the formation of its first leaves till its death, it is 

 constantly absorbing moisture from the soil through 

 the roots, and as constantly parting with it by the 

 leaves. The water thus collected from the soil, con- 

 tains carbonic acid, ammonia, and such saline matters 

 as are present in the soil. If the leaves of the plant 

 are exposed to the action of light, the carbonic acid 

 and ammonia are decomposed, together with a portion 

 of the water, and organic matter is formed. 



731. During the night, or in the absence of light, 

 this change takes place but imperfectly ; and hence, 

 then, the water absorbed by the roots, which is still 

 given oif by the leaves, carries with it a considerable 

 portion of the gaseous matter collected from the 

 soil. 



732. The exact ofiice in the nutrition of plants, 

 performed by the saline substances they absorb, is as. 

 yet but imperfectly known. Some plants appear to 

 require particular substances, and it is known that 

 certain substances cannot be formed by plants, unless 

 the soil contains particular saline matters. All plants 

 contain more or less lime, as well as other bases, such 

 as potash and soda ; these, of course, are never in 



