Sap, in botany, denotes the juice of plants, which is prepared by the moisture absorbed by their roots and leaves, whence it is circulated throughout every part, so as to constitute their nourishment.

The sap of vegetables has been compared to the chyle of animals: according to Dr.Darwin, the former consists of sugar, water, and mucilage, together with other transparent solutions; for instance, those of phosphorus, carbon, and calcareous earth. The sap, when first absorbed by the roots, is thin and watery, but, during its progress, it acquires more consistence ; and, when it a, rives at the leaves, it is assimilated to the nature of the plant.

The circulation of this juice has generally been supposed to be performed in an uniform manner: it appears, however, from the experiments of Mr. FaiRchild, a late eminent gardener, that it has an irregular motion, directly contrary to its primary course j a discovery which is of considerable importance in horticulture. This agreeable and salubrious art may thus not only be improved, but also great advantage may be derived from the general application of this principle ; as barren trees may now be rendered fruitful, and old or decaying ones restored to their original vigour. - See Juice.