Stems 3 Functions: Support leaves and reproductive structures Support leaves and reproductive structures Internal transport Internal transport Produce new tissue Produce new tissue

External Stuctures

Internal Structures: Monocots Most herbaceous Most herbaceous Exception: Palms Exception: Palms Vascular bundles Vascular bundles Ground tissue Ground tissue No lateral meristems No lateral meristems

Internal Structures: Herbaceous Dicots Cortex Cortex Vascular tissue Vascular tissue Some have vascular cambium Some have vascular cambium Annual vs. Perrenial Annual vs. Perrenial Pith Pith

Woody Stems of Eudicots Primary tissue arranged like that in herbaceous stem Primary tissue arranged like that in herbaceous stem Secondary growth Secondary growth Girth Girth Vascular cambium Vascular cambium Cork cambium Cork cambium Once secondary growth begins, internal structure changes Once secondary growth begins, internal structure changes

Secondary Growth Vascular cambium become continuous Vascular cambium become continuous Cells in cambium produce daughter cells in 2 directions Cells in cambium produce daughter cells in 2 directions After division, 1 cell remains meristematic After division, 1 cell remains meristematic

As secondary tissue forms 1 o xylem and phloem become separated from each other As secondary tissue forms 1 o xylem and phloem become separated from each other 1 o tissue outside cylinder of growth crushed or torn apart 1 o tissue outside cylinder of growth crushed or torn apart 2 o xylem and phloem contain same types of cells and perform same function as primary tissue 2 o xylem and phloem contain same types of cells and perform same function as primary tissue Rays connect 2 o xylem and phloem and allow for lateral transport of material Rays connect 2 o xylem and phloem and allow for lateral transport of material

Cork Cambium Arises from parenchyma cells in outer cortex Arises from parenchyma cells in outer cortex Produces periderm Produces periderm Cork cells form to the outside Cork cells form to the outside Dead at maturity Dead at maturity Waterproof & Impermeable to gases Waterproof & Impermeable to gases Cork parechyma form to inside Cork parechyma form to inside

Common Wood Terms Softwood Softwood Hardwood Hardwood Sapwood Sapwood Heartwood – Older wood, in center Heartwood – Older wood, in center

Annual Rings Used to determine the age of a tree in temperate climate Used to determine the age of a tree in temperate climate Difference between springwood and summerwood Difference between springwood and summerwood Springwood – large diameter of conducting cells, few fibers Springwood – large diameter of conducting cells, few fibers Summerwood – narrower conducting cells, more fibers Summerwood – narrower conducting cells, more fibers