ray

(secondary ray) A radial line of parenchyma cells in the secondary xylem and phloem, derived from the ray initials of the vascular cambium. The ray system of gymnosperms often also contains tracheids, distinguished from the ray parenchyma by their bordered pits and lack of protoplast. Rays may be uniseriate (one cell thick in tangential longitudinal section) or multiseriate (several cells thick in tangential longitudinal section). Compare medullary ray.