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Flowering Plant Vegetative Structures BIOL 1108 I. Primary Tissues Unlike animals, most plants have indeterminate growth, meaning that they grow throughout life. Primary growth increases the length of stems and roots and produces the plant’s three primary tissue types: epidermal, ground, and vascular tissue. Epidermal tissue consists of a single layer of cells that covers plant surfaces. Ground tissue makes up most of the plant body; its functions include storage and photosynthesis. Vascular tissue functions in support and transport. It includes xylem, which transports water, and phloem, which transports sugars and other organics. Plant tissues arise from undifferentiated meristem tissue that persists throughout the plant’s life. Apical meristems are found at the tips of roots and stems and produce primary growth. Examine the following specimens and slides available in the lab and identify the tissues and structures mentioned. Useful figures from the textbook (Freeman, 6th ed.) are shown in parentheses. A. Root Structure Roots anchor plants in the soil, absorb water and nutrients, and store various plant products. Using your textbook, identify the function of the following root structures: epidermis root hairs root cap apical meristem cortex vascular cylinder Examine the monocot and dicot roots on display. Notice that dicots typically have long, vertical taproots, while monocots have fibrous root systems. Look at the prepared slide of a longitudinal section of onion (Allium) root and identify the following structures: root cap, apical meristem, epidermis. (see Figure 34.16b, p. 719 and Figure 34.18a, p. 720) Can you see any root hairs? Look at the prepared slide of a cross section of buttercup (Ranunculus) root and identify the following structures: epidermis, cortex, vascular cylinder. (see Figure 35.6, p. 732) B. Stem Structure Stems support the leaves of the plant, store various products, and contain vascular tissue for transporting water and nutrients between the roots and leaves. Using your textbook, identify the function of the following stem structures: node internode apical bud lateral (axillary) bud cuticle cortex pith vascular bundle Examine the Coleus plant on display and identify the following structures: stem, node, internode, apical bud, lateral (axillary) bud (see Figure 34.1, p. 705). Look at the prepared slide of a longitudinal section of a Coleus stem and identify the following structures: apical meristem at tip of shoot and lateral buds (bud primordium), immature leaves (leaf primordium). (see Figure 34.16a, p. 719) Look at the prepared slide of a cross section of an alfalfa (Medicago) stem and identify the following structures: epidermis, cuticle (if visible), cortex, pith, vascular bundles. (see Figure 34.19a, p. 721). What differences do you notice between stem and root structure? C. Leaf Structure The primary function of leaves is photosynthesis. Leaves do not have apical meristems. Using your textbook, identify the function of the following leaf structures: blade petiole stomata guard cells mesophyll vein Examine the Coleus plant and identify the blade and petiole of a leaf. Look at the prepared slide of a mature lilac (Syringa) leaf and compare it to the leaf model in the lab. Identify the following structures: epidermis, cuticle, stomata, guard cells, veins. Note the arrangement of the mesophyll cells. The layers of elongated cells on the upper part of the leaf make up the palisade mesophyll. The more loosely arranged cell layer is the spongy mesophyll. It contains air spaces for O2 and CO2 circulation. Look at the demo slide of the underside of a Tradescantia leaf and identify the stomata. Are they open or closed? II. Secondary Growth In addition to primary growth some plants experience secondary growth, which increases the thickness of stems and roots. Secondary growth produces secondary xylem, or wood, and secondary phloem, which forms the inner layer of bark. Both of these tissues are formed from a meristem tissue called the vascular cambium, which is located between the layers of secondary xylem and phloem. Typically, new layers of secondary xylem and phloem are produced during each growing season. The secondary xylem persists, producing growth rings in the wood. Look at the prepared slide of a cross section of a basswood (Tilia) stem. Identify the pith, secondary xylem, vascular cambium, and secondary phloem. (see Figure 34.20, p. 722) How many annual rings of wood are present? How old was this plant?