1126. It is necessary, or at least advantageous, to supply food artificially ; and hence the origin of manuring. All organised matters are capable of being converted into the food of plants; but mineral substances are also essential, and plants will not grow well in any soil in which the earthy matters they require are deficient. Manuring with decayed vegetable and animal matter is an obvious imitation of the operations of nature, every where observable by the decaying herbage of herbaceous plants, or the fallen leaves of trees, rotting into dust or vegetable mould about their roots: and by the effect of the dung left by animals.
