14 5. Sugar-conducting cells of the phloem BOT 1015. Sugar-conducting cells of the phloemSieve-tube members:Lack a nucleus, ribosomes, vacuoleCells separated by perforated sieve plates – allow sugar movement
26 BOT 101Cell divisionOccurs in only in meristems!
27 Meristems = Two types of meristems: Apical meristem – BOT 101Meristems=Two types of meristems:Apical meristem –Lateral meristems – extend lengthwise along the axis of the stem & roots. Responsible for growth in girth in older parts of the plant (called secondary growth). Exist only in perennials
29 Arrangement of Primary Tissues in Roots BOT 101Arrangement of Primary Tissues in RootsEpidermis –Stele –Ground tissue – mostly parenchyma cells of the cortex – area between the stele & epidermis; stores food & takes up minerals.Endodermis – single cell layer between cortex & stele. Selective barrier for uptake of soil solution contents into vascular system.
37 Secondary Growth Two lateral meristems: BOT 101Secondary GrowthTwo lateral meristems:Vascular cambium – produces secondary xylem (= wood) & phloemCork cambium – replaces the epidermis with cork: tough, thick cover for stems, roots.
38 Secondary growth of stems BOT 101Secondary growth of stemsVascular cambium – layer of cells between primary xylem & primary phloem. Puts on successive layers of secondary phloem to outside & secondary xylem to inside =====> stem widensWood = accumulation of secondary xylem. Dead at maturity, contains lignin
39 BOT 101What is bark?“bark” =Cork continually sloughs off
43 Three types of life cycles: BOT 101Three types of life cycles:Annual –Biennial – complete life cycle in two years (first year = vegetative, second year = reproductive). Some need a cold winter period to initiate flowering from vegetative state. Ex. carrotsPerennial – live year after year, do not die after reproduction. Examples: trees, shrubs, some grasses. Causes of death = fire, disease