BIO 2137 Lecture Notes - Lecture 12: Vascular Tissue, Herbaceous Plant, Tracheid
21 Jan 2021
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Aerial roots (absorption of moisture from air) The shoot system of a plant includes stems, leaves, and (in angiosperms) flowers. Produces a succession of leaf and bud primordia. Vascular tissue in isolated strands (vascular bundles) separated by parenchyma cells. Each strand consists of phloem (outside) and xylem (inside) separated by a layer or procambium. Procambium disappears in herbaceous species; it becomes vascular cambium in woody species. Fascicular cambium produces radial rows of secondary xylem and phloem to thicken the stem. Rays = parenchyma cells formed by interfascicular cambium. Rays are used as a pathway for water and food between xylem and ploem. Secondary growth crushes phloem, epidermis and eventually cortex. Only small amount of phloem is functional. Secondary xylem accumulates year after year = wood. Many conifers (like pinus) produce resin, wood contains resin ducts. The leaves are the primary sites of photosynthesis in most plants.
