Botany · Ch 10 — Secondary Growth
Tissue Lineages During Secondary Growth in Dicot Stem and Root
Tissue Lineages During Secondary Growth in Dicot Stem and Root
The various secondary tissues covered across this chapter - secondary xylem, secondary phloem, the rays that run through them, and the periderm's phellem and phelloderm - do not all trace back to one single meristem cell type; they descend along two separate lineages within the vascular cambium and cork cambium respectively, and those lineages differ slightly between stem and root. In both organs, the vascular cambium's fusiform initials give rise to the axial xylem and axial phloem, while its ray initials give rise to the xylem rays and phloem rays - but the vascular cambium itself has different upstream origins in each organ: in the stem it forms from the procambium (fascicular cambium) together with the interfascicular cambium, while in the root it forms from the pericycle together with conjunctive tissue. The cork cambium (phellogen), likewise, gives rise to phellem outward and phelloderm inward (with lenticels forming within the phellem) in both organs, but again starts from different tissue in each: mainly the epidermis and cortex in the stem, versus mainly the pericycle in the root. Tracin …
What this figure shows. A pair of flowcharts (one for dicot stem, one for dicot root) tracing tissue lineage from primary structure through the pre-structure of secondary growth to the final secondary structure. For the stem: Procambium branches into Fascicular cambium and (via medullary-ray parenchyma) Interfascicular cambium, together forming the Vascular cambium (built of Fusiform initials and Ray initials), which gives rise to Axial Xylem and Xylem rays inward and Axial Phloem and Phloem rays outward; separately, the stem's Epidermis and Cortex give rise to the Cork cambium (Phellogen), producing Phellem (cork) outward and Phelloderm (secondary cortex) inward, with Lenticels forming in the phellem. For the root: Pericycle and Conjunctive tissue (below the Phloem) give rise to the Vascular cambium, again built of Fusiform and Ray initials and giving rise to the same Axial Xylem/Xylem rays and Axial Phloem/Phloem rays; the root's Pericycle also separately gives rise to the Cork cambium (Phellogen), producing Phellem and Phelloderm as in the stem. No numbered figure caption was printed wit …