bio

Vascular cambium

The cylindrical layer of dividing cells between wood and bark, producing xylem inward and phloem outward. It is the organ that makes a woody tree in the modern sense, and it is not universal: it appears in progymnosperms in the late Devonian, is present in conifers and most broadleaved plants, and is entirely absent from monocots. Palms and yuccas reach tree stature another way — they thicken by a primary meristem, embedding closed vascular bundles through soft tissue like rebar in concrete.