CONDUCTION (Lat. conduetio, union, from conducerc, to lead together, from cow-, together duccrc, to lead, connected with Goth.
AS. trot, OHG. ziohan, Ger. rich en, to draw). In botany, a term applied to the transfer of water, foods, and other materials front one part of the plant body to another. In the smaller plants a sufficient amount of water can be supplied to cover evaporation and other needs, and the foods can be transferred. by relatively slow processes of dif fusion and osmosis (qq.v.). In the larger plants, however, the amount of water and foods to be moved, and the relatively great distances to he traversed, have brought about the development of a system of tissues, arranged in elongated strands or in layers, specially adapted to facilitate trans fer, and known as the conducting system. These are for water chiefly the xylem, or wood bundles, and for foods chiefly the phloem, or bast bundles, or perhaps the latex vessels. The xylem and
phloem bundles are usually associated, running side by side in the stems, the xylem either toward the centre, or with a phloem bundle also on the central side of it, or surrounded by the phloem. In the roots the primary xylem bundles are be tween the phloem bundles, but by secondary thick ening with age the same position as in stems is reached. So frequent is this association that the two bundles are usually described as re gions of one fibrovascular bundle (q.v.). These bundles form a connected system of strands, con tinuous, through the stem, from youngest root to youngest leaf. In the leaves the bundles run in the larger ribs, and constitute the smaller veins, becoming more and more slender. The final branches join with others to form a fine network, or end blindly among the green tissues, the xylem bundles being the last to disappear.