SAP

The fluid which is absorbed by the roots from the earth, then sent upwards into the stem, and afterwards conveyed from the leaves, where it is a imilated and altered, to the bark. In its crude state it consists of little except water holding earthy and gaseous matter in solution, especially carbonic acid; but as it rises through the ti ue of the stem it di olves the secretions it meets with in its course, and thus acquires new properties, so that by the time it reaches the leaves it is entirely dififerent from its state when it first enters the root. The course taken by the sap in its pa age through the stem is by the whole of the ti ue mcluded within the bark, provided it is all permeable; but as, in many plants, the central part of the stem becomes choked up with solid matter deposited in the ti ue, it usually happens, especially in trees, that the course of the sap is confined to the outer part of the wood, hence called sapwood. It is not certainly known through what kind of ti ue the upward motion of the sap takes place, but it is probable that it is carried onwards through all the tubes and ve els of the wood and their intercellular pa ages. The dotted ve els of the wood seem more especially destined to fulfil this office when the sap is in rapid motion; but as they afterwards become empty, while the ascent of the sap continues, there can be no doubt that the woody tubes or pleurenchyma offer the most constant means by which the sap is conveyed. In Fortification, sap is a trench or approach made under cover of gabions, . [s. 1092]