Xylem cells, specifically those found in secondary xylem—the wood formed as a plant stem thickens—are produced from a specialized layer of actively dividing cells known as the vascular cambium.
Production in Secondary Xylem
According to the provided information, the production of vessel elements, a key type of xylem cell responsible for water transport, occurs during this secondary growth phase.
The process originates within the vascular cambium, where a long cell oriented along the axis of the stem, called a fusiform initial, plays a crucial role.
Here’s how it happens:
- The vascular cambium contains various types of initial cells.
- Fusiform initials are specifically responsible for producing the elongated cells found in the axial system of the secondary xylem, such as vessel elements.
- A fusiform initial cell undergoes cell division.
- Crucially, this division occurs along its length, meaning the new cell wall is formed parallel to the longest axis of the stem.
- One of the resulting daughter cells differentiates into a new vessel element (or other axial xylem cells like tracheids or fibers, though the reference specifically mentions vessel elements), while the other daughter cell often remains a fusiform initial, allowing the cambium to continue producing new cells.
This continuous division and differentiation by the fusiform initials in the vascular cambium are what lead to the increase in stem diameter and the formation of wood (secondary xylem).
