| abscission zone | area at the base of the petiole where cellular breakdown leads to leaf and fruit drop |
| absorbing roots | fine, fibrous roots that take up water and minerals. Most absorbing roots are within the top 12" (30 cm) of soil. |
| aerial roots | aboveground roots. Usually adventitious in nature and sometimes having unique adaptive functions. |
| adventitious bud | bud arising from a place other than a leaf axil or shoot tip, usually as a result of hormonal triggers. |
| angiosperm | polant with seeds borne in an ovary. Consists of two large groups: monocotyledons (grasses, palms, and related plants) and dicotyledons (most woody trees, shrubs, herbaceous plants, and related plants). Contrast with gymnosperms. |
| anthocyanin | red or purple pigment responsible for those colors in some parts of trees and other plants. Compare to carotenoid. |
| antitranspirant | substance applied to the foliage of plants to reduce water loss (transpiration). |
| apical bud | bud at the tip of a twig or shoot. |
| apical dominance | condition in which the terminal bud inhibits the growth and development of the lateral buds on the same stem formed during the same season. |
| apical meristem | growing point at the tips of shoots and roots. |
| apoplasm | free spaces in plant tissue. Includes cell walls and intracellular spaces. |
| auxin | plant hormone or substance that promotes or regulates the growth and development of plants. Produced at sites where cells are dividing, primarily in the shoot tips. Auxin-like compounds may be synthetically produced. |
| axial transport | movement of water, minerals, or photosynthates longitudinally within a tree. |
| axillary bud | bud in the axil of a leaf. Lateral bud. |
| branch bark ridge | raised strip of bark at the top of a branch union, where the growth and expansion of the trunk or parent stem and adjoining branch push the bark into a ridge. |
| branch collar | area where a branch joins another branch or trunk that is created by the overlapping vascular tissues from both the branch and the trunk. Typically enlarged at the base of the branch |
| bud | (1) small lateral or terminal protuberance on the stem of a plant that may develop into a flower or shoot. (2) undeveloped flower or shoot containing a meristematic growing point. |
| buttress root | roots at the trunk base that help support the tree and equalize mechanical stress. |
| cambium | thin layer(s) of meristematic cells that give rise (outward) to the phloem and (inward) to the xylem, increasing stem and root diameter. |
| carbohydrate | compound, combining carbon, hydrogen, and oxygen, that is produced by plants as a result of photosynthesis. Sugars and starches. |
| carotenoid | yellow, orange, or red pigment responsible for those colors in some parts of trees and other plants. Compare to anthocyanin. |
| cellulose | complex carbohydrate found in the cellular walls of the majority of plants and algae and certain fungi. |
| chlorophyll | green pigment of plants found in chloroplasts. Captures the energy of the sun and is essential in photosynthesis. |
| chloroplast | specialized organelle found in some cells. Site of photosynthesis. |
| CODIT | Compartmentalization of Decay in Trees |
| companion cell | specialized cell in the angiosperm phloem derived from the same parent cell as the closely associated, immediately adjacent sieve-tube member. |
| compartmentalization | natural defense process in trees by which chemical and physical boundaries are created that act to limit the spread of disease and decay organisms. |
| cork cambium | meristematic tissue from which the corky, protective outer layer of bark is formed. |
| cuticle | waxy layer outside the epidermis of a leaf that reduces water loss and resists insect damage. |
| cytokinin | plant hormone involved in cell division, leaf expansion, and other physiological process. Compounds with cytokinin-like activity may be synthetically produced. |
| deciduous | tree or other plant that sheds all of its leaves according to a genetically scheduled cycle as impacted by climate factors (usually during the cold season in temperate zones). Contrast evergreen. |
| decurrent | rounded or spreading growth habit of the tree crown. Contrast with excurrent. |
| differentiation | process in the development of cells in which they become specialized for various functions. |
| diffuse porous | pattern of wood development in which the vessels and vessel sizes are distributed evenly throughout the annual ring. Contrast with ring porous. |
| dormant | in a period of dormancy |
| ecology | study of the relationships among organisms and other living and nonliving elements of their environment. |
| epicormic | arising from a latent adventitious bud (growth point). Usually in reference to a shoot. |
| evergreen | tree or other plant that does NOT shed all of its foliage annually. Contrast with deciduous. |
| excurrent | tree growth habit characterized by a central leader and pyramidal crown. Contrast with decurrent. |
| fiber | (1) elongated, tapering, thick-walled cell that provides strength to wood. (2) smallest component of a rope. |
| frond | large, divided leaf structures found in palms and ferns. |
| geotropism | plant growth produced as a response to the force of gravity, either positive, as in the direction of gravity (roots) or negative, as in opposite the direction of gravity (shoots). |
| growth ring | rings of xylem that are visible in a cross section of the stem, branches and roots of some trees. In temperate zones, the rings typically represent one year of growth and are sometimes referred to as annual rings. |
| guard cell | pair of specialized cells that regulate the opening and closing of a stomate. |
| gymnosperm | plants with exposed seeds, usually within cones. Contrast with angiosperm. |
| heartwood | wood that is altered (inward) from sapwood and provides chemical defense against decay-causing organisms and continues to provide structural strength to the trunk. Trees may or may not have heartwood. Contrast with sapwood. |
| included bark | bark that becomes embedded in a crotch (union) between branch and trunk or between codominant stems. Causes a weak structure. |
| inflorescence | cluster of flowers |
| internode | region of the stem between two successive nodes. Contrast with node. |
| lateral bud | vegetative bud on the side of a stem. Contrast with terminal bud. |
| lateral root | root that arises by cell division in the pericycle of the parent root and then penetrates the cortex and epidermis. |
| leaf axil | point of attachment of a leaf petiole to a stem. |
| lenticel | small opening in the bark that permits the exchange of gases. |
| lignin | organic substance that impregnates certain cell walls to thicken and strengthen the cell to reduce susceptibility to decay and pest damage. |
| meristem | undifferentiated tissue in which active cell division takes place. Found in the root tips, buds, cambium, cork cambium and latent buds. |
| monocot | see monocotyledon |
| monocotyledon | plant with an embryo that has on seed leaf (cotyledon). Examples are grasses and palms. Contrast with dicotyledon. |
| mycorrhizae | symbiotic association between certain fungi and the roots of a plant. |
| node | slightly enlarged portion of a stem where leaves and buds arise. Contrast with internode. |
| osmosis | diffusion of water through a semi-permeable membrane from a region of higher water potential (lower salt concentration) to a region of lower water potential (higher salt concentration). |
| parenchyma cell | thin-walled, living cells essential in photosynthesis, radial transport, energy storage and production of protective compounds |
| periderm | the outer layers of tissue of woody roots and stems, consisting of the cork cambium and the tissues produced by it, such as bark. |
| petiole | stalk or support axis of a leaf. |
| phloem | plant vascular tissue that transport photosynthates and growth regulators. Situated on the inside of the bark, just outside the cambium. Is bidirectional (transports up and down). Contrast with xylem. |
| photosynthate | general term for the sugars and other carbohydrates produced during photosynthesis. |
| photosynthesis | process in green plants (and in algae and some bacteria) by which light energy is used to form glucose (chemical energy) from water and carbon dioxide. |
| phototropism | influence of light on the direction of plant growth. Tendency of plants to grow toward light |
| plant growth regulator | compound effective in small quantities that affects the growth and/or development of plants. May be naturally produced (hormone) or synthetic. See plant hormone. |
| plant hormone | substance produced by a plant that, in low concentrations, affects physiological processes such as growth and development, often at a distance from the substance point of origin. See plant growth regulator. |
| primary growth | root and stem growth in length. Occurs at the apical meristems and lateral meristems of all vascular plants |
| propagation | process of increasing plant numbers, both sexually and asexually. |
| radial transport | lateral movement of substances, perpendicular to the longitudinal axis of the tree or stem. |
| ray | parenchyma tissues that extend radially across the xylem and phloem of a tree and function in transport, storage, structural strength and defense. |
| reaction zone | natural boundary formed chemically within a tree to separate damaged wood from existing healthy wood. Important in the process of compartmentalization. |
| respiration | in plants, process by which carbohydrates are converted into energy by using oxygen. |
| ring porous | pattern of wood development in which the large-diameter vessels are concentrated in the earlywood. Contrast with diffuse porous. |
| root crown | area where the main roots join the plant stem, usually at or near ground level. Root collar. |
| root initiation zone | region at the base of a palm stem where lateral roots emerge. |
| root mat | dense network of roots near the base of a palm. |
| sapwood | outer wood (xylem)that is active in longitudinal transport of water and minerals. Contrast with heartwood. |
| secondary growth | increase in root and stem girth or diameter. Occurs at lateral meristems in some vascular plants such as dicots. |
| sieve cell | long, slender phloem cell in gymnosperms. |
| specialized phloem cells involved in photosynthate transport. Exist only in angiosperms. | sieve tube element |
| sink | plant part that uses or stores more energy than it produces. |
| sinker root | downward-growing roots that provide anchorage and take up water and minerals. Especially useful during periods of drought. |
| source | in physiology, plant part that produces carbohydrates. Mature leaves are sources. |
| stomata | small pores, between two guard cells on the undersides of leaves and other green plant parts, through which gasses are exchanged and water loss is regulated. |
| symbiosis | association of two different types of living organisms that is often, but not always, beneficial to each. |
| symplasm | entire mass of protoplasm of all the cells in a plant, interconnected by plasmodesmata. Symplast. Contrast with apoplasm. |
| tap root | central, vertical root growing directly below the main stem or trunk that may or may not persist into plant maturity. |
| temperate | region lying between the tropics and the poles that has relatively moderate temperatures. |
| terminal bud | bud at the tip of a twig or shoot. |
| tracheid | elongated, tapering xylem cell adapted for the support and transport of water and elements. |
| transpiration | water vapor loss through the stomata of leaves. |
| tropism | tendency of growth or variation of a plant in response to an external stimulus such as gravity (geotropism) or light (phototropism). |
| vessel | end-to-end, tubelike, water-conducting cells in the xylem of angiosperms. |
| xylem | main water-and mineral-conducting (unidirectional, up only) tissue in trees and other plants. Provides structural support. Arises (inward) from the cambium and becomes wood after lignifying. Contrast with phloem. |
