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How do fusiform initials and ray initials build the tissues of wood?

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Tall giant sequoia trees with reddish bark and thick trunks rise closely together in a dense forest at Sequoia National Park, California. — Tree A stand of giant sequoia trees (*Sequoiadendron giganteum*) in Sequoia National Park, California.

In woody plants, the vascular cambium is a lateral meristem responsible for secondary growth, which creates the wood and inner bark of a tree. This cambium consists of two distinct types of cells that divide tangentially to build these tissues:12

Fusiform initials: These are elongated, tapering cells that give rise to the axial (vertical) system of the plant. This system includes the primary conducting and supporting elements, such as tracheids, vessel elements, and fibers, which are oriented parallel to the long axis of the tree trunk.123
Ray initials: These are smaller, isodiametric (squat) cells that produce the radial (horizontal) system of the wood and bark. These cells form vascular rays, which are oriented perpendicular to the axial cells. This radial system is essential for the lateral transport and storage of water and carbohydrates.123

Through these divisions, the cambium produces secondary xylem toward the inside and secondary phloem toward the outside, with significantly more xylem being produced to provide structural support and conduction.132