Botany - Stem

• stem - organ of the plant that holds structures such as leaves, flowers, and fruits. Unlike roots, stems have nodes and internodes
• node - the area/region where the leaves are attached
• internode - the area/region between nodes
• petiole - a stalk that attaches the leaf blade to the stem
• stipules - paired leaf-like appendages at the base of the petiole
• lenticels - dark spots/elevations that allow gas exchange in the stem
• 2 types of bud

  • axillary bud
  • terminal bud
• bud - an undeveloped shoot contains embryonic meristem
• axillary bud - bud located in the axil. may later develop into braches/ into flowers
• terminal bud - often present at the tip of each twig. normally produces tissue that extends the length of the twig
• leaf scar - scar left by a fallen leaf
• bundle scar - scars that mark the location of the water conducting tissue located within the leaf scars
• apical meristem - tissue in which cells acitvely divide
• leaf primordia - tiny embryonic leaves that will develop into mature leaves
• the cells of the apical meristem undergo mitosis and soon 3 primary meristem develop from it:

  • protoderm
  • procambium
  • ground meristem
• protoderm - gives rise to epidermis
• procambium - located inferior of the protoderm, produces primary xylem and primary phloem
• ground meristem - produces 2 tissues composed of parenchyma cells.
• the parenchyma tissue in the center of the stem is the pith
• a complex region found next to the epidermis is the cortex
• vascular cambium - one of the 2 lateral meristems
• vascular cambium - referred simply as the cambium
• vascular cambium - cells here continue to divide indefinitely
• vascular cambium - produces secondary tissues that add to the girth of the stem instead of its length
• cells in vascular cambium produced becomes tracheids, vessel elements, fibers (secondary xylem) or they become sieve tubes members, companion cells (secondary phloem)
• cork cambium is also referred as phellogen
• cork cambium - produces boxlike cork cells impregnated suberin (waxy substance that makes the cells impervious to moisture)
• cork cells are produced annually but die shortly after they are formed
• cork tissue makes up the outer bark of woody plants
• cork cambium functions in reducing water loss and in protecting the stem against mehcanical injury
• the vascular bundle of herbaceous eudicot stems are arranged in a circle around a central pith
• stem - cross section

  epidermis - an outer covering, provides protection in herbaceous stems as it does in roots
• stem - cross section: cuticle - a waxy layer that reduces water loss from the stem surface, usually covers the epidermis
• stem - cross section: cortex - a cylinder several cells thick that is part of a plant's ground tissue system. may contain parenchyma, collenchyma, and scelerenchyma cells
• stem - cross section

  vascular tissues - provide conduction and support
• stem - cross section

  stele - central cylinder of a stem that includes xylem, phloem and often pith
• vascular cambium - single layer of cells which is sandwich between the xylem and phloem. it is a lateral meristem that is responsible for secondary growth
• Stems are much stronger than roots. The thick walls of

  tracheids and vessel elements in xylem help support the plant.
• vessel elements are short and wide and have perforations
• tracheids are spindle shaped and have pits