Carpel - One of the modified leaves of the flower that encloses the ovules; this term sometimes refers to the entire female reproductive organ, otherwise known as the pistil.

Chlorophyll - A green pigment, necessary for photosynthesis, that is found in the chloroplasts of plants.

Corolla - The flower whorl that contains the petals.

Cotyledon - An embryonic leaf characteristic of angiosperms; monocot embryos have one, and dicot embryos have two.

Dicot - An flowering plant (angiosperm) that possesses two cotyledons during embryonic development.

Embryonic Axis - Component of the embryo made up of the epicotyl (future shoot) and hypocotyl (future root).

Endosperm - A substance, formed from a triploid nucleus in angiosperm reproduction, that nourishes a developing embryo within a seed.

Epicotyl - The portion of the embryonic axis above the attachment of the cotyledons; develops into the shoot.

Epidermal - Refers to the cells which lie on the outer surface of an organism.

Fibrous Roots - A system of many small, branching roots (none of which predominates) that spread out in the top few centimeters of soil; characteristic of monocots.

Filament - The stalk of the stamen, the male reproductive organ of the flower.

Guard cell - One of the two epidermal cells that surround the stoma of the leaf and regulate gas exchange by opening and closing the stoma.

Gynoecium - The innermost flower whorl, containing the pistil(s), the female reproductive organ(s) of the flower.

Heartwood - Wood made up of xylem that is no longer functioning in nutrient transport.

Herbaceous Dicot - A plant, usually an annual, with a soft, non-woody stem.

Hypocotyl - The portion of the embryonic axis below the point of attachment of the cotyledons; develops into the root.

Mesophyll - The internal tissue of a leaf; specialized for photosynthesis.

Monocot - An flowering plant (angiosperm) that possesses one cotyledon during embryonic development.

Ovary - In plants, the protective structure that holds the ovules and surrounds the angiosperm seed; composed of carpels and found at the base of the pistil.

Ovule - Structure that contains the female gametophyte and gametes; after fertilization, develops into a seed.

Palisade Layer - A layer of the mesophyll. The palisade layer is made up chloroplasts arranged in columns and located just below the epidermis of plant cells. In most plants, the palisade layer exists only on the top of the life, where the leaf receives sunlight. In some plants, in which leaves hang down and both sides of the leaves receive sunlight, the palisade layer is on both sides of the leaf.

Parenchyma cells - The most common type of plant cell. Parenchyma are not particularly specialized, are usually round, and can be found in leaves, stems, and roots. Parenchyma cells are alive at maturity.

Perianth - Nonreproductive portion of a flower comprised of the calyx and corolla.

Petal - Modified leaf, usually brightly colored, that attracts insects and other pollen- carrying animals to the flower.

Phloem - Vascular tissue composed of conductile cells that are living at maturity; transports the products of photosynthesis throughout the plant body.

Photosynthesis - The process by which plants and other autotrophic organisms convert light energy into organic materials.

Pistil - The female reproductive organ of the flower, composed of a stigma, style, and ovary; sometimes called the carpel.

Pith - Plant tissue located at the center of the stem; functions partly in nutrient storage.

Pollen Grain - The male gametophyte of gymnosperms and angiosperms.

Ray - Horizontal passageways in the stems of woody dicots that lead from the phloem to the pith at the center of the stem.

Root - The part of a plant beneath the soil; responsible for collecting water and minerals from the soil, storing nutrients, and securing the plant to the ground.

Sapwood - Wood made up of xylem tissue that is active in the vascular system.

Sepal - Green, leaf-like structure that encloses and protects the unopened flower bud.

Spongy Layer - A layer of the mesophyll. The spongy layer consists of chloroplasts and parenchyma cells, and relatively large intercellular spaces. It is far less ordered than the palisade layer, and the intercellular spaces are important in gas exchange and transpiration.

Stamen - The male reproductive organ of the flower, comprised of an anther and filament.

Stigma - The top part of the pistil, where pollen grains are received.

Stoma - A very small epidermal pore, surrounded by two guard cells, through which gases diffuse in and out of a leaf.

Style - The shaft of the pistil that leads from the stigma down into the ovary.

Taproot - A single dominant root (often with several smaller secondary roots branching off of it) that extends deep into the soil; characteristic of dicots.

Transpiration - The process by which a plant loses water to its environment through evaporation.

Triploid - Having three sets of chromosomes.

Vascular Bundle - Vascular passageways comprised of xylem and phloem "bundled" together.

Vascular Cambium - Tissue that produces new vascular cells; lies between the xylem and phloem in dicot stems.

Vascular System - Mechanism of internal water and nutrient transport, made up of the vascular tissues xylem and phloem, that is characteristic of tracheophytes.

Vascular Tissue - A conductile component (either xylem or phloem) of the system that transports food and nutrients throughout the plant body.

Whorl - One of the four sets of modified leaves (calyx, corolla, androecium, or gynoecium) that perform various functions on the flower.

Woody Dicot - A plant, usually a perennial, with a woody stem; most trees are woody dicots.

Xylem - Vascular tissue composed of conductile cells that are dead at maturity; transports water and dissolved minerals upwards from the roots to the shoot.

Zygote - The diploid product of fertilization that develops into an embryo.

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