Xylogenesis

Xylogenesis refers to the biological process by which wood is formed. It is a key aspect of secondary growth in plants, primarily woody dicots and gymnosperms, leading to the thickening of stems and roots. This process is mediated by the vascular cambium, a lateral meristematic tissue. The vascular cambium is a layer of undifferentiated cells located between the xylem and phloem. In response to various environmental and hormonal signals, these cambial cells divide periclinally, meaning their division planes are parallel to the surface of the stem or root.

One daughter cell from each cambial division typically remains a cambial cell, ensuring the continued production of new cells. The other daughter cell differentiates to form either secondary xylem (wood) towards the inside or secondary phloem towards the outside. The secondary xylem is composed of various cell types, including tracheids, vessel elements, fibers, and parenchyma cells, all of which contribute to the structural support and water transport functions of wood. The rate of xylogenesis can be influenced by factors such as water availability, temperature, and day length, leading to the formation of annual growth rings in many temperate species, where differences in cell size and density between spring and summer growth are evident.