| Term | Definition |
|---|
| adventitious | A term describing any plant organ that grows in an atypical location, such as roots growing from stems. |
| annual | A flowering plant that completes its entire life cycle in a single year or growing season |
| axillary bud | A structure that has the potential to form a lateral shoot, or branch. The bud appears in the angle formed between a leaf and a stem. |
| bark | All tissues external to the vascular cambium, consisting mainly of the secondary phloem and layers of periderm. |
| biennial | A flowering plant that requires two years to complete its life cycle. |
| blade | The flattened portion of a typical leaf |
| bundle sheath | A protective covering around a leaf vein, consisting of one or more cell layers, usually parenchyma. |
| collenchyma cell | A flexible plant cell type that occurs in strands or cylinders that support young parts of the plant without restraining growth. |
| companion cell | A type of plant cell that is connected to a sieve-tube member by many plasmodesmata and whose nucleus and ribosomes may serve one or more adjacent sieve-tube members. |
| cork cambium | A cylinder of meristematic tissue in woody plants that replaces the epidermis with thicker, tougher cork cells |
| cortex | Ground tissue that is between the vascular tissue and dermal tissue in a root or dicot stem. |
| cuticle | A waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial plants. |
| derivative | A new cell that is displaced from an apical meristem and continues to divide until the cells it produces become specialized |
| dermal tissue system | The outer protective covering of plants |
| determinate growth | A type of growth characteristic of most animals and some plant organs, in which growth stops after a certain size is reached. |
| endodermis | The innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the cortex and the vascular cylinder. |
| epidermis | The dermal tissue system of nonwoody plants, usually consisting of a single layer of tightly packed cells. |
| fiber | A lignified cell type that reinforces the xylem of angiosperms and functions in mechanical support; a slender, tapered sclerenchyma cell that usually occurs in bundles. |
| fibrous root system | A root system common to monocots consisting of a mat of thin roots spreading out below the soil surface. |
| fusiform initial | a cell within the vascular cambrium that produces elongated cells such as tracheids, vessel elements, fibers, and sieve-tube members. |
| ground tissue system | Plant tissues that are neither vascular nor dermal, fulfilling a variety of functions, such as storage, photosynthesis, and support. |
| guard cells | The two cells that flank the stomatal pore and regulate the opening and closing of the pore. |
| heartwood | Older layers of secondary xylem, closer to the center of a stem or root, that no longer transport xylem sap. |
| herbaceous | Nonwoody |
| indeterminate growth | A type of growth characteristic of plants, in which the organism continues to grow as long as it lives. |
| initial | A cell that remain within an apical meristem as a source of new cells. |
| internode | A segment of a plant stem between the points where leaves are attached. |
| lateral meristem | A meristem that thickens the roots and shoots of woody plants. |
| lateral root | A root that arises from the outermost layer of the pericycle of an established root. |
| leaf | Main photosynthetic organ of most plants |
| leaf primordia | Fingerlike projections along the flanks of a shoot apical meristem, from which leaves arise. |
| leaf trace | A small vascular bundle that extends from the vascular tissue of the stem through the petiole and into a leaf. |
| lenticel | Small raised area in the bark of stems and roots that enables gas exchange between living cells and the outside air. |
| meristem | Plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth. |
| meristem identity gene | A plant gene that promotes the switch from vegetative growth to flowering. |
| mesophyll | The ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis. |
| morphogenesis | Development of body shape and organization |
| node | Where the leaves are attached to a stem |
| organ | A specialized center of body function composed of several different types of tissues. |
| organ identity gene | Plant homeotic gene that uses positional information to determine which emerging leaves develop into which types of floral organs. |
| palisade mesophyll | One or more layers of elongated photosynthetic cells on the upper part of a leaf |
| parenchyma cell | A relatively unspecialized plant cell type that carries out most of the metabolism, synthesizes and stores organic products, and develops into a more differentiated cell type. |
| pattern formation | The ordering of cells into specific three-dimensional structures, an essential part of shaping an organism and its individual parts during development. |
| perennial | A flowering plant that lives for many years. |
| pericycle | The outermost layer of the vascular cylinder of a root, where lateral roots originate. |
| periderm | The protective coat that replaces the epidermis in plants during secondary growth, formed of the cork and cork cambium. |
| petiole | The stalk of a leaf, which joins the leaf to a node of the stem. |
| phloem | Vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant |
| pit | A thinner region in the walls of tracheids and vessels where only primary wall is present |
| pith | Ground tissue that is internal to the vascular tissue in a stem; in many monocot roots, parenchyma cells that form the central core of the vascular cylinder |
| plasticity | An organism’s ability to alter or mold itself in response to local environmental conditions. |
| polarity | A lack of symmetry. Structural differences in opposite ends of an organism or structure, such as the root end and shoot end of a plant. |
| positional information | Signals to which genes regulating development respond, indicating a cell’s location relative to other cells in an embryonic structure. |
| preprophase band | Microtubules in the cortex (outer cytoplasm) of a cell that are concentrated into a ring. |
| primary growth | Growth produced by apical meristems, which lengthen stems and roots. |
| primary plant body | The tissues produced by apical meristems, which lengthen stems and roots. |
| protoplast | The contents of a plant cell except the cell wall |
| ray initial | A cell within the vascular cambrium that produces xylem and phloem rays, radial file that consist mostly of parenchyma cells. |
| root | An organ in vascular plants that anchors the plant and enables it to absorb water and nutrients from the soil. |
| root cap | A cone of cells at the tip of a plant root that protects the apical meristem. |
| root hair | A tiny extension of a root epidermal cell, growing just behind the root tip and increasing surface area for absorption of water and minerals. |
| sapwood | Outer layers of secondary xylem that still transport xylem sap. |
| sclereid | A short, irregular sclerenchyma cell in nutshells and seed coats and scattered through the parenchyma of some plants. |
| sclerenchyma cell | A rigid, supportive plant cell type usually lacking protoplasts and possessing thick secondary walls strengthened by lignin at maturity. |
| secondary growth | Growth produced by lateral meristems, which thickens the roots and shoots of woody plants. |
| secondary plant body | The tissues produced by the vascular cambium and cork cambium, which thicken the stems and roots of woody plants. |
| shoot system | The aerial portion of a plant body, consisting of stems, leaves, and (in angiosperms) flowers. |
| sieve plate | An end wall in a sieve-tube member, which facilitates the flow of phloem sap in angiosperm sieve tubes. |
| sieve-tube member | A living cell that conducts sugars and other organic nutrients in the phloem of angiosperms. They form chains called sieve tubes. |
| spongy mesophyll | Loosely arranged photosynthetic cells located below the palisade mesophyll cells in a leaf. |
| stele | The vascular tissue of a stem or root. |
| stem | A vascular plant organ consisting of an alternating system of nodes and internodes that support the leaves and reproductive structures. |
| stoma | A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant. |
| systems biology | An approach to studying biology that aims to model the dynamic behavior of whole biological systems. |
| taproot system | A root system common to eudicots consisting of one large, vertical root (the taproot) that produces many smaller lateral, or branch, roots. |
| terminal bud | Embryonic tissue at the tip of a shoot, made up of developing leaves and a compact series of nodes and internodes. |
| tracheid | A long, tapered water-conducting cell that is dead at maturity and is found in the xylem of all vascular plants. |
| vascular bundle | A strand of vascular tissues (both xylem and phloem) in a stem or leaf. |
| vascular cambium | A cylinder of meristematic tissue in woody plants that adds layers of secondary vascular tissue called secondary xylem (wood) and secondary phloem. |
| vascular cylinder | The central cylinder of vascular tissue in a root. |
| vein | A vascular bundle in a leaf. |
| vessel element | A short, wide, water-conducting cell found in the xylem of most angiosperms and a few nonflowering vascular plants; Dead at maturity; aligned end to end to form micropipes called vessels |
| vessel | A continuous water-conducting micropipe found in most angiosperms and a few nonflowering vascular plants. |
| xylem | Vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from roots to the rest of the plant. |
| zone of cell division | The zone of primary growth in roots consisting of the root apical meristem and its derivatives. New root cells are produced in this region. |
| zone of elongation | The zone of primary growth in roots where new cells elongate, sometimes up to ten times their original length. |
| zone of maturation | The zone of primary growth in roots where cells complete their differentiation and become functionally mature. |
| protonema | A mass of green, branched, one-cell-thick filaments produced by germinating moss spores. |
| rhizoid | Fibrous organ that anchors nonvascular plants to the root |
| sorus | A cluster of sporangia on a fern sporophyll |
| strobili | The technical term for clusters of sporophylls known commonly as cones, found in most gymnosperms and some seedless vascular plants. |
| sporocyte | A diploid cell, also known as a spore mother cell, that undergoes meiosis and generates haploid spores. |
| calyptra | A protective cap of gametophyte tissue that wholly or partially covers an immature capsule in many mosses. |
| phragmoplast | An alignment of cytoskeletal elements and Golgi-derived vesicles across the midline of a dividing plant cell. |
| peat | Extensive deposits of undecayed organic material formed primarily from the wetland moss Sphagnum. |
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