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How do fusiform initials and ray initials produce different wood tissues?
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wood
Temperate softwoods (left column) and hardwoods (right column), selected to highlight natural variations in colour and figure: (A) Douglas fir, (B) sugar pine, (C) redwood, (D) white oak, (E) American sycamore, and (F) black cherry. Each image shows (from left to right) transverse, radial, and tangential surfaces. Click on an individual image for an enlarged view.
The vascular cambium is responsible for the secondary growth of woody plants, producing wood (secondary xylem) and inner bark (secondary phloem) through the activity of two distinct types of meristematic cells:
- Fusiform initials: These are elongated, tapering cells that give rise to the axial (vertical) system of the plant. The cells produced by these initials are arranged parallel to the long axis of the trunk and include tracheary elements, fibers, and sieve cells, which are primarily responsible for structural support and the longitudinal conduction of water and nutrients.1234
- Ray initials: These are squat, isodiametric cells that produce the radial (horizontal) system of the wood and bark, known as vascular rays. These cells are oriented perpendicular to the axial system and function primarily in the translocation and storage of food and water between the inner bark and the wood.1254
Together, these two systems create the organized structure of wood, with the axial system providing vertical transport and strength, and the radial system facilitating horizontal movement and storage.14