Slide 27: cross section of another eudicot stem in its first year of growth. A ray system can be noted, extending throughout the secondary xylem and phloem. From outside in, locate the epidermis, cortex (with tightly packed collenchyma cells close to the epidermis and parenchyma cells inside), primary phloem, secondary phloem, vascular cambium, secondary xylem, and primary xylem. Note the vascular rays in the secondary xylem and secondary phloem. Vascular rays are radial strands of parenchyma cells that function as pathways for lateral transport of materials and as storage areas. Ray cells are produced by the ray initials in the vascular cambium.