- abscisic acid (ABA)
- plant hormone that induces dormancy in seeds and other organs
- abscission
- physiological process that leads to the fall of a plant organ (such as leaf or petal drop)
- adventitious root
- aboveground root that arises from a plant part other than the radicle of the plant embryo
- apical bud
- bud formed at the tip of the shoot
- apical meristem
- meristematic tissue located at the tips of stems and roots; enables a plant to extend in length
- auxin
- plant hormone that influences cell elongation (in phototropism), gravitropism, apical dominance, and root growth
- axillary bud
- bud located in the axil: the stem area where the petiole connects to the stem
- bark
- tough, waterproof, outer epidermal layer of cork cells
- bulb
- modified underground stem that consists of a large bud surrounded by numerous leaf scales
- Casparian strip
- waxy coating that forces water to cross endodermal plasma membranes before entering the vascular cylinder, instead of moving between endodermal cells
- chromophore
- molecule that absorbs light
- collenchyma cell
- elongated plant cell with unevenly thickened walls; provides structural support to the stem and leaves
- companion cell
- phloem cell that is connected to sieve-tube cells; has large amounts of ribosomes and mitochondria
- compound leaf
- leaf in which the leaf blade is subdivided to form leaflets, all attached to the midrib
- corm
- rounded, fleshy underground stem that contains stored food
- cortex
- ground tissue found between the vascular tissue and the epidermis in a stem or root
- cryptochrome
- protein that absorbs light in the blue and ultraviolet regions of the light spectrum
- cuticle
- waxy covering on the outside of the leaf and stem that prevents the loss of water
- cuticle
- waxy protective layer on the leaf surface
- cytokinin
- plant hormone that promotes cell division
- dermal tissue
- protective plant tissue covering the outermost part of the plant; controls gas exchange
- endodermis
- layer of cells in the root that forms a selective barrier between the ground tissue and the vascular tissue, allowing water and minerals to enter the root while excluding toxins and pathogens
- epidermis
- single layer of cells found in plant dermal tissue; covers and protects underlying tissue
- ethylene
- volatile plant hormone that is associated with fruit ripening, flower wilting, and leaf fall
- fibrous root system
- type of root system in which the roots arise from the base of the stem in a cluster, forming a dense network of roots; found in monocots
- gibberellin (GA)
- plant hormone that stimulates shoot elongation, seed germination, and the maturation and dropping of fruit and flowers
- ground tissue
- plant tissue involved in photosynthesis; provides support, and stores water and sugars
- guard cells
- paired cells on either side of a stoma that control stomatal opening and thereby regulate the movement of gases and water vapor
- intercalary meristem
- meristematic tissue located at nodes and the bases of leaf blades; found only in monocots
- internode
- region between nodes on the stem
- jasmonates
- small family of compounds derived from the fatty acid linoleic acid
- lamina
- leaf blade
- lateral meristem
- meristematic tissue that enables a plant to increase in thickness or girth
- lenticel
- opening on the surface of mature woody stems that facilitates gas exchange
- megapascal (MPa)
- pressure units that measure water potential
- meristem
- plant region of continuous growth
- meristematic tissue
- tissue containing cells that constantly divide; contributes to plant growth
- negative gravitropism
- growth away from Earth’s gravity
- node
- point along the stem at which leaves, flowers, or aerial roots originate
- oligosaccharin
- hormone important in plant defenses against bacterial and fungal infections
- palmately compound leaf
- leaf type with leaflets that emerge from a point, resembling the palm of a hand
- parenchyma cell
- most common type of plant cell; found in the stem, root, leaf, and in fruit pulp; site of photosynthesis and starch storage
- pericycle
- outer boundary of the stele from which lateral roots can arise
- periderm
- outermost covering of woody stems; consists of the cork cambium, cork cells, and the phelloderm
- permanent tissue
- plant tissue composed of cells that are no longer actively dividing
- petiole
- stalk of the leaf
- photomorphogenesis
- growth and development of plants in response to light
- photoperiodism
- occurrence of plant processes, such as germination and flowering, according to the time of year
- phototropin
- blue-light receptor that promotes phototropism, stomatal opening and closing, and other responses that promote photosynthesis
- phototropism
- directional bending of a plant toward a light source
- phyllotaxy
- arrangement of leaves on a stem
- phytochrome
- plant pigment protein that exists in two reversible forms (Pr and Pfr) and mediates morphologic changes in response to red light
- pinnately compound leaf
- leaf type with a divided leaf blade consisting of leaflets arranged on both sides of the midrib
- pith
- ground tissue found towards the interior of the vascular tissue in a stem or root
- positive gravitropism
- growth toward Earth’s gravitational center
- primary growth
- growth resulting in an increase in length of the stem and the root; caused by cell division in the shoot or root apical meristem
- rhizome
- modified underground stem that grows horizontally to the soil surface and has nodes and internodes
- root cap
- protective cells covering the tip of the growing root
- root hair
- hair-like structure that is an extension of epidermal cells; increases the root surface area and aids in absorption of water and minerals
- root system
- belowground portion of the plant that supports the plant and absorbs water and minerals
- runner
- stolon that runs above the ground and produces new clone plants at nodes
- sclerenchyma cell
- plant cell that has thick secondary walls and provides structural support; usually dead at maturity
- secondary growth
- growth resulting in an increase in thickness or girth; caused by the lateral meristem and cork cambium
- sessile
- leaf without a petiole that is attached directly to the plant stem
- shoot system
- aboveground portion of the plant; consists of nonreproductive plant parts, such as leaves and stems, and reproductive parts, such as flowers and fruits
- sieve-tube cell
- phloem cell arranged end to end to form a sieve tube that transports organic substances such as sugars and amino acids
- simple leaf
- leaf type in which the lamina is completely undivided or merely lobed
- sink
- growing parts of a plant, such as roots and young leaves, which require photosynthate
- source
- organ that produces photosynthate for a plant
- statolith
- (also, amyloplast) plant organelle that contains heavy starch granules
- stele
- inner portion of the root containing the vascular tissue; surrounded by the endodermis
- stipule
- small green structure found on either side of the leaf stalk or petiole
- stolon
- modified stem that runs parallel to the ground and can give rise to new plants at the nodes
- strigolactone
- hormone that promotes seed germination in some species and inhibits lateral apical development in the absence of auxins
- tap root system
- type of root system with a main root that grows vertically with few lateral roots; found in dicots
- tendril
- modified stem consisting of slender, twining strands used for support or climbing
- thigmomorphogenesis
- developmental response to touch
- thigmonastic
- directional growth of a plant independent of the direction in which contact is applied
- thigmotropism
- directional growth of a plant in response to constant contact
- thorn
- modified stem branch appearing as a sharp outgrowth that protects the plant
- tracheid
- xylem cell with thick secondary walls that helps transport water
- translocation
- mass transport of photosynthates from source to sink in vascular plants
- transpiration
- loss of water vapor to the atmosphere through stomata
- trichome
- hair-like structure on the epidermal surface
- tuber
- modified underground stem adapted for starch storage; has many adventitious buds
- vascular bundle
- strands of stem tissue made up of xylem and phloem
- vascular stele
- strands of root tissue made up of xylem and phloem
- vascular tissue
- tissue made up of xylem and phloem that transports food and water throughout the plant
- venation
- pattern of veins in a leaf; may be parallel (as in monocots), reticulate (as in dicots), or dichotomous (as in ginkgo biloba)
- vessel element
- xylem cell that is shorter than a tracheid and has thinner walls
- water potential (Ψw)
- the potential energy of a water solution per unit volume in relation to pure water at atmospheric pressure and ambient temperature
- whorled
- pattern of leaf arrangement in which three or more leaves are connected at a node