AGRICULTURAL TEXT-BOOK. 



Calcium, - - Oxygen, Lime. 



Magnesium, - Magnesia, 



Aluminum, - &quot; Alumina, (Clay.) 



Silicon, - Silica, (Sand.) 



Iron and ) ( Oxides. 



Manganese, j - Sulphur, ( Sulphurets. 



94. With the exception of Iodine, the above appear to be es 

 sential to the composition of all cultivated plants. 



95. The organic and inorganic elements are chemically com 

 bined, and are always undergoing change. They perhaps never 

 exist in plants in a simple form. 



96. These inorganic materials may be so carried away from 

 the soil by injudicious cropping that at last the land refuses to 

 bear grain, until they are replaced, or, in other words, till the 

 land is manured. Again, manure, by its chemical action, may 

 set free these elements in the soil which were previously unfit 

 for absorption by roots. To recapitulate 



97. A fertile soil consists of three earths: (a,) Sand; (bj 

 Clay, and (c,) Lime, mechanically combined; (d,) of four 

 gasses, forming organic matter ; and (e,) of eleven or twelve in 

 organic elements, in small quantities, chemically combined. 



98. Practically, the difference between a rich and an impov 

 erished soil is this : A rich soil contains every thing a plant 

 requires in a soluble state, ready to be at once absorbed by the 

 roots of the plant. A worn-out soil contains the same constitu 

 ents but in an insoluble state, not capable of being dissolved in 

 water, and therefore unable to enter into the roots. 



99. On whatever soil a plant is grown, if it shoots up in a 

 healthy manner, and fairly ripens its seed, the quantity and qual 

 ity of the ash is nearly the same. 



100. No two plants of a different order contain the same 

 quantity and quality of inorganic matter. The more widely two 

 plants differ in their natural character, (e. g. turnips and wheat,) 

 the wider will be the difference between their constituents. 



