578 THE PHILOSOPHY OF FARMING. 
elements and substances alone. The exceeding 
minute delicacy of the tissues of this structure 
renders it all but impossible for solid matter to 
enter the system. The principal kinds of aerial 
and fluid matter are carbonic acid gas, or air, a 
little azote, or nitrogen gas, and water; which 
substances may be said to correspond with the 
stone, or brick, timber, and mortar of a building. 
And, singular as it may seem to the unitiated 
mind, the almost countless kinds of vegetable 
produce, with their specific properties, are the 
result of differently arranging and combining 
these three substances, and the four atomic 
elements which they contain; and exactly as 
these elements and substances, under certain 
conditions of the soil, are present in abundance, 
or otherwise, when we cultivate plants, the 
increase of what is profitable for us is promoted, 
and the decrease of what is noxious to us accele- 
rated, and the noxious qualities almost nullified 
and rendered void. Hence, as the food of plants 
consists mainly of fluid and aerial elements, the 
soil in which plants grow can be but a medium of 
that growth, or a recipient of the elements and 
substances of such food or material as the plant 
requires. To know how the soil acts in this 
capacity, and how its capabilities so to act may 
