The Xylem
Explanation:
The Xylem
It is a woody fabric of the upper vegetables that conducts water and inorganic salts upwards throughout the plant and also provides mechanical support. In the leaves, flowers and young stems, the xylem is combined with phloem in the form of conductive vascular bundles. The roots have a central cylinder of xylem. The xylem formed from the growth points of stems and roots is called primary. But in addition, the division of the cambium cells, located between the xylem and the phloem, can produce new secondary xylem or xylem; This division gives rise to new xylem cells inward at the roots and outward in almost all stems. Some plants have very little secondary xylem or none, in contrast to woody species; The botanical term xylem means wood.
The xylem can contain three types of elongated cells: tracheids, vascular elements or vessels (tracheas) and fibers. At maturity, when they perform transport functions, all these cells are dead. Tracheids are elongated cells with thick walls characterized by the presence of very well defined thin areas called pits. Vascular elements or vessels are specialized tracheids whose terminal walls are crossed by one or several pores; A vertical series of vascular elements that form a continuous tube is called a vessel. The fibers are specialized tracheids of very thickened wall that hardly perform transport functions and that serve to increase the mechanical strength of the xylem.
The xylem of the oldest species from the point of view of evolution, such as ferns and conifers, is formed by tracheids. In almost all angiosperms (flowering plants), the xylem also contains well-developed vessels and fibers. As the sequences of specialization of all these tissue elements are observed quite clearly, the study of the xylem provides important clues to elucidate the evolution of higher plants.
