Ch25: The Shoot: Primary Structure And Development

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mesophyll

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The ground tissue (parenchyma) of a leaf, located between the layers of epidermis; mesophyll cells generally contain chloroplasts

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apical meristem

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The meristem at the tip of the root or shoot in a vascular plant

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mesophyte

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[Gk. mesos, middle, + phyton, plant] A plant that requires an environment that is neither too wet nor too dry

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blade

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The broad, expanded part of a leaf; the lamina

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phytomeres

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A succession of repeated developmental units, consisting of a node with its attached leaf (or leaves), the internode below the leaf (or leaves), and the bud (or buds) at the base of the internode

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hydrophyte

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[Gk. hydro, water, + phyton, plant] A plant that depends on an abundant supply of moisture or that grows wholly or partly submerged in water

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petiole

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The stalk of a leaf

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interfascicular region

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Tissue region between vascular bundles in a stem. Also called a pith ray

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leaf scar

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A scar left on a twig when a leaf falls

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homeotic mutation

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A mutation that changes organ identity so that the wrong structures appear in the wrong place or at the wrong time

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leaf trace gap

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In seed plants, region of parenchyma tissue in the primary vascular cylinder of a stem above the point of departure of the leaf trace or traces

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homeotic genes

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Genes affecting floral organ identity

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leaf trace

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That part of a vascular bundle extending from the base of the leaf to its connection with a vascular bundle in the stem

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phyllotaxis

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The arrangement of leaves on a stem. Also called phyllotaxy

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herbaceous

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Referring to nonwoody plants

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bundle-sheath extension

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A plate of ground tissue extending from a bundle sheath of a vein in the leaf mesophyll to the upper or lower epidermis, or both; may consist of parenchyma, collenchyma, or sclerenchyma

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bundle sheath

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Layer or layers of cells surrounding a vascular bundle; may consist of parenchyma or sclerenchyma cells, or both

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abscission

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The dropping off of leaves, flowers, fruits, or other plant parts, usually following the formation of an abscission zone

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abscission zone

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The area at the base of a leaf, flower, fruit, or other plant part containing tissues that play a role in the separation of the plant part from the plant body

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bulliform cells

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Large epidermal cells present in longitudinal rows in grass leaves; believed to be involved in the mechanism of rolling and unrolling or folding and unfolding of the leaves. Also called motor cells

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cladophyll

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[Gk. klados, shoot, + phyllon, leaf] A branch resembling a foliage leaf

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corm

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A thickened underground stem, upright in position, in which food is accumulated, usually in the form of starch

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bulb

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A short underground stem covered by enlarged and fleshy leaf bases containing stored food

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founder cells

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The group of cells from which leaf primordia and root primordia are initiated

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palisade parenchyma

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A leaf tissue composed of columnar chloroplast-bearing parenchyma cells with their long axes at right angles to the leaf surface

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stipule

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An appendage, often leaflike, on either side of the basal part of a leaf, or encircling the stem, in many kinds of flowering plants

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sheath

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(1) The base of a leaf that wraps around the stem, as in grasses; (2) a tissue layer surrounding another tissue, such as a bundle sheath

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tunica-corpus

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The organization of the shoot apex of most angiosperms and a few gymnosperms, consisting of one or more peripheral layers of cells (the tunica layers) and an interior (the corpus). The tunica layers undergo surface growth (by anticlinal divisions), and the corpus undergoes volume growth (by divisions in all planes)

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shoot

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The aboveground portions, such as the stem and leaves, of a vascular plant

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sessile

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[L. sessilis, of or fit for sitting, low, dwarfed] Attached directly by the base; referring to a leaf lacking a petiole or to a flower or fruit lacking a pedicel

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pith ray

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See interfascicular region

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pith

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The ground tissue occupying the center of the stem or root within the vascular cylinder; usually consists of parenchyma

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stem bundle

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Vascular bundle belonging to the stem

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xerophyte

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[Gk. xeros, dry, + phyton, plant] A plant that has adapted to arid habitats

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rachis

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[Gk. rachis, backbone] The main axis of a spike; in ferns, the axis of a leaf (frond), from which the pinnae arise; in compound leaves, the extension of the petiole corresponding to the midrib of an entire leaf

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spongy parenchyma

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A leaf tissue composed of loosely arranged, chloroplast-bearing cells

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major veins

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The larger leaf vascular bundles, which are associated with ribs; they are largely involved in the transport of substances into and out of the leaf

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netted venation

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The arrangement of veins in the leaf blade that resembles a net; characteristic of the leaves of all angiosperms except for monocots. Also called reticulate venation

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minor veins

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The small leaf vascular bundles, located in the mesophyll and enclosed by a bundle sheath; involved in distribution of the transpiration stream and uptake of the products of photosynthesis

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parallel venation

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The pattern of venation in which the principal veins of the leaf are parallel or nearly so; characteristic of monocots

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sympodium

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pl. sympodia A stem bundle and its associated leaf traces

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tendril

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[L. tendere, to extend] A modified leaf or part of a leaf or a modified stem forming a slender, coiling structure that aids in support of the plant's stems; found only in some angiosperms

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stolon

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[L. stolo, shoot] A stem that grows horizontally along the ground surface and may form roots, such as the runners of a strawberry plant. Also called a runner

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transition region

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The region in the primary plant body showing transitional characteristics between structures of root and shoot

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rhizome

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A more or less horizontal underground stem

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vein

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A vascular bundle forming part of the framework of the conducting and supporting tissue of a leaf or other expanded organ

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tuber

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[L. tuber, swelling] An enlarged, short, fleshy underground stem, such as that of the potato