Ground Tissues Collenchyma and Sclerenchyma

Lab. No. 2 Ground tissues Collenchyma and Sclerenchyma Slides Prepared 1- Coleus stem c.s 2- Syringa leaf c. s 3- Nymphea lef c.s 4- Tilia stem c.s 5- Zea stem c.s. 6- Quercus wood three sections (Demonstration only one slide) 7- Helianthus stem c.s Fresh specimen 1) Washingtonia leaf 2) Pear ‫اجاص‬ 3) Apple * 4) Broad bean ‫فول‬ 5) Olive leaves 6) Senseviria plant 7) Vitis (Grape) stem branch (maceration) 1 Lab. No. 2 Ground tissues Collenchyma and Sclerenchyma Collenchyma -Collenchyma is closely related to parenchyma, defined as living cells (normally) with unevenly thickened primary walls. - The thickening of the primary cell wall is uneven, depending on this thickening there are three types of collenchyma (Angular collenchyma, Lamellar collenchyma and Lacunar collenchyma) -Function in mechanical support in growing organs. - In some instances, after organ elongation has ceased, collenchyma is converted to sclerenchyma with deposition of secondary, lignified cell walls. -usually collenchyma occupy peripheral position in the organs it present in, either directly beneath the epidermis or few layers removed from the epidermis in stems and in leaf petiole. In leaf blade occurs in ribs especially the large ones. Rarely occur in roots. 1- Coleus stem C.S. Prepared slide Notice: - the polyhedral (isodiametric ) parenchyma cells in cortex. (shape of cells, type of cell wall, intercellular spaces between cells, if it contains crystals or chloroplasts) - Collenchyma in cortex immediately inside epidermis. (Determine type of collenchyma, shape of cells) 2 2-Syringa leaf C.S. Prepared slide - notice Collenchyma cells in ribs (mid rib) of this leaf and determine the type of collenchyma. Sclerenchyma  A tissue of cells with thickened secondary (lignified) cell walls and non living protoplast at maturity.  Function mainly in mechanical support.  Classified usually into two types: sclereids & fibers 1-Sclereids: Isodiametric- elongated (shorter than fibers) Lignified cell wall with pits Occur in all plant parts Depending on shape: - Brachysclereids (stone cells) isodiametric 1) Hoya wax plant prepare a stem c.s , you may stain using Toluidine Blue , notice brachysclerides in pith and cortex and with phloem , try to notice pits. Pyrus (pear) fruit flesh, press the flesh of fruit on a slide to see stone cells (brachysclerides) -It is preferred to use Toluidine blue dye. - Macrosclereids (rod cells) columnar 2) Malus (apple), prepare a temporary slide of apple fruit endocarp, partly macerated, notice the columnar cells. Osteosclereids (bone cells) elongated with enlarged ends 3) bean seeds. Prepare partly macerated seed coat of beans to see bone cells. Astrosclereids (star cells) cells with arms 4) study Nymphaea (water lily) leaf c.s. Trichosclereids (filiform sclereids) hair like, may be branched 5) Prepare thin c.s as possible as you can from olive leaf and try to notice trichosclereids in mesophyll 3 2-Fibers Highly elongated cells with pointed ends Narrow lumen, thick secondary cell wall Present in leaves and are oriented in same direction as viens. There are 2 types of fibers: Extraxylary fibers - not in the xylem (wood), their wall have pits (mostly simple pits) Often present in the phloem : study prepared slide of 6) Tilia Stem c.s notice phloem fibers or around the veins (perivascular fibers)as a cap : study prepared slide of 7) Helianthus stem c.s notice caps of fibers around the vascular bundles [perivascular bundle cap] (Notice too different types of collenchyma in the cortex of this stem) or a sheath, study prepared slide of 8) Zea stem c.s and notice sheath of fibers around the vascular bundles [ perivascular bundle sheath] Xylary fibers - xylem (wood) fibers ,2 types Septate fibers: with thick partitions or septa , usually retain protoplast at maturity and store starch. Study macerated wood of 9) Vitis (grape) stem and libriform fibers: present in bundles, as long cells with thick walls. Study macerated wood of 10) Quercus or prepared slide of L.S. stem of Quercus Leaf fibers: Study macerated leaves (boiled in weak KOH) of 11) Sensevieria or Washingtonia Examples of fibers used commercially: Linum (flax) phloem fibers Cocos (coconut) fibers from husk of fruit Gossypium (cotton) seed hairs that are commercially called fibers but botanically are epidermal hairs. 4