Sap

Sap, a term or popular, rather than of scientific. vegetable physiology, applying to the various juices of plants. Firstly, the drops of water containing some soluble matter that form in the vacuoles of the protoplasm of young cells are known as the watery cell-sap. [CELL.] Secondly, the liquid food taken in by the roots from the soil, consisting of water with dissolved mineral matters, is known as the unelaborated sap. It is forced upwards in early spring by root-pressure, this being known as the rise or ascent of the sap. Its upward course, under the influence of root-pressure and, at a later stage, of transpiration, is by the vessels or tracheids in the young wood. Thirdly, the milky latex (q.v.) and other liquids, such as the contents or the sieve-tubes, which form part of the elaborated sap, and contain sugar, starch, albuminoid and other matters, the results of assimilation and metabolism, are also termed sap. Their course is towards all growing parts. This, together with the course of the unelaborated sap which is mainly upward, is mistakenly known as the circulation of the sap. As there is no heart or central pumping-station, and no return of liquid to its starting-point, there is no true circulation in plants.