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The physiology of stems



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The physiology of stems

  1. 1. The Physiology of Stems
  2. 2. CONDUCTION OF MATERIALS BY STEMS Conduction by Xylem Chief function of xylem is the upward conduction of water and dissolved substances (sap). These dissolved substances are chiefly mineral salts from the soil; also, foods previously stored in the roots and stem may be conducted upward in spring in woody plants.
  3. 3. Ascents of Saps Root Pressure This explains the exudation of sap from the stumps of decapitated or detopped plants including those of trees that were newly felled.
  4. 4. Capillary Attraction 1)water rises in narrow tubes due to the force of surface tension • It stated that it is the capillary action of narrow xylem tubes and it is further supported by atmospheric pressure
  5. 5. Atmospheric Pressure Forces water up through the conducting cells of the xylem, as it supports a mercury column in barometer.
  6. 6. Action of Living Cells Suggested that living cells adjoining the conduction cells of the xylem force water upward, possibly by some sort of pumping action.
  7. 7. Imbibition in Cell Walls of Xylem The cell walls of xylem cells absorb water ny imbibition, but imbibitional force is not sufficient to explain either the rapidity or magnitude of sap rise.
  8. 8. Transpiration Pull and Water Cohesion This explains that the upward movement of water is mainly due to the creation of a negative force or tension attributed to the continuous evaporation of water at the surfaces of leaves in the process of transpiration. As molecule after molecule of water evaporates through the stomata, it creates a pulling action on the next molecules of water in the transpiration stream.
  9. 9. The transpiration pull is similar to the suction force when drinking some fluid from a bottle or glass with a straw. Water can also be sucked into a pippette with the use of an ordinary rubber aspirator or with a common medicine dropper.
  10. 10. Conduction by Phloem The chief evidence of phloem is the downward conduction of foods manufactured in the leaves. Some upward conduction of minerals and foods occurs in the phloem.
  11. 11. Conduction of Vascular Rays In which extend ought radially in stems extend through the xylem and also into the phloem. These rays bring about the transverAse (crosswise) conduction of foods, minerals, water, and gases.
  12. 12. Other Functions of stems Food Storage Occurs chiefly in the parenchyma cells of cortex, rays, and pith, and also in the phloem and xylem parenchyma. Climbing stems Tendrils, such as those of grapes, or twining stems such as those of morning glories, are examples.
  13. 13. Food Manufacture stems ehich contain chlorophyll, such as those of most herbaceous plants and of cacti, manufacture food. Reproduction Production is brought about by runners, by the branching rhizomes , by the formation of new bulbs and corns from older ones, etc.
  14. 14. PRACTICAL APPLICATIONS OF A KNOWLEDGE OF STEM STRUCTURE AND PHYSIOLOGY PRUNING In pruning away diseased , broken or otherwise undesired branch, the cut should be made as close to the main branch as parallel to i, in order that the growth tissues sorrounding the wound may form new tissues to heal the wound.
  15. 15. GIRDLING Is the removal of a complete ring of bark . Girdling stops the downward passage of food, which collects above the girdle. Practiced in order to; 1. Produce large fruits 2. Kill trees, in clearing land. 3.Produce more flowersin the season following girdle.
  16. 16. GRAFTING Is a horticultural practice in which two freshly cut stem surfaces are bound together in such fashion that their cells grow together; thus there is formeda union between the two pieces of stem.