botany ebony

Long-distance transport of sugars and other solutes in phloem

Translocation

Plant region that exports sugars into the phloem

Source

Plant region that receives sugars for growth or storage

Sink

Movement of sucrose into phloem at a source

Phloem loading

Movement of sucrose from phloem into sink tissues

Phloem unloading

Model in which source-to-sink pressure differences drive phloem sap

Pressure-flow hypothesis

Movement of phloem sap driven by a hydrostatic pressure gradient

Bulk flow

Plants adapted to dry environments and limited water.

Xerophytes

Plants adapted to freshwater or waterlogged aquatic conditions.

Hydrophytes

Plants adapted to saline soils and high salt levels.

Halophytes

Loss of water vapor from plant aerial surfaces.

Transpiration

Physical model explaining xylem ascent by transpiration-generated tension.

Cohesion–tension theory

Attraction among water molecules that maintains a continuous water column.

Cohesion

Attraction of water molecules to xylem walls.

Adhesion

Pulling force produced by water evaporation from leaves.

Transpiration pull

Water movement across a selectively permeable membrane down water-potential gradient.

Osmosis

Soil-cation exchange process promoted by roots releasing H⁺.

Ion exchange

Main ion whose guard-cell uptake promotes osmotic water entry and stomatal opening.

Potassium (K⁺)

Guard-cell condition with high water pressure that opens the stoma.

Turgidity

Hormone linked to stomatal closure during drought.

Abscisic acid (ABA)

Pair of cells regulating stomatal opening and closure

Guard cells

Epidermal cells that assist guard cells when present

Subsidiary cells

Photosynthetic ground tissue between the upper and lower leaf epidermis

Mesophyll

Dense, elongated photosynthetic cells often beneath the upper epidermis

Palisade mesophyll

Loose photosynthetic tissue with air spaces for internal gas diffusion

Spongy mesophyll

Grass-leaf epidermal cells involved in leaf rolling under water stress

Bulliform cells

Modified leaf with a sharp protective tip, as in cactus

Leaf spine

Sharp defensive structure derived from a stem or branch, not a leaf

Thorn

Sharp outgrowth of epidermal and superficial cortical tissue

Prickle

Flattened photosynthetic petiole or rachis replacing a normal leaf blade

Phyllode

False stem of banana formed mainly from overlapping leaf sheaths

Pseudostem

Fossilized tree resin sometimes enclosing insects

Amber

Broad photosynthetic blade of a leaf

Lamina

Stalk connecting the leaf blade to the stem

Petiole

Main axis of a compound leaf bearing its leaflets

Rachis

Small stalk attaching an individual leaflet to the rachis

Petiolule

Leaf blade divided into distinct leaflets

Compound leaf

Leaf feature at its base that helps distinguish a whole leaf from leaflets

Axillary bud

Leaf vein pattern forming a branching network, common in dicots

Reticulate venation

Leaf vein pattern in which major veins run approximately parallel

Parallel venation

Pore through which leaf gas exchange and water loss occur

Stoma

Woody monocot grass used for furniture, flooring, and as a timber substitute

Bamboo

Growth that increases a stem’s diameter by lateral meristem activity

Secondary growth

Vascular tissue produced inward by the vascular cambium, forming wood

Secondary xylem

Vascular tissue produced outward by the vascular cambium

Secondary phloem

Protective tissue formed outward by cork cambium

Phellem (cork)

Complete secondary protective system: phellem, phellogen, and phelloderm

Periderm

All woody-stem tissues external to the vascular cambium

Bark

Younger outer wood region that still conducts water

Sapwood

Older inner wood region that generally no longer conducts water

Heartwood

Seasonally distinct layers of secondary xylem seen in a trunk cross-section

Growth rings

Removal of a complete ring of bark that interrupts sugar transport

Girdling

long narrow xylem conducting cell with tapered ends and pits

tracheid

xylem conducting cell connected end-to-end with perforation plates

vessel element

Living phloem conducting cell that loses its nucleus at maturity

sieve-tube element

nucleated cell providing metabolic support to sieve-tube element

companion cell

openings in the end walls of the vessel elements

perforation plates

perforated end walls connecting phloem sieve-tube elements

sieve plates

sugar-rich fluid transported within sieve-tube elements

phloem sap

Points on a stem where buds or leaves attach

nodes

stem segment between successive nodes

internodes

Bud in the axil between a leaf and its stem

axillary bud

Developing leaf structures near a shoot apical meristem

Leaf primordial

Arrangement of scattered vascular bundles typical of monocot stems

atacotstele

arrangement of vascular bundles in the ring typical of dicot stem

eustele

bundle with xylem and pholem side by side and no cambium between them.

closed collateral vascular bundle

bundle with xylem, phloem and vascular cambium between them

open collateral vascular bundle

stem xylem maturation pattern: protoxylem inward, metaxylem outward

endarch

cavity left by the breakdown of protaoxylem in some monocot stems, such as maize

protaoxylem lacuna

Root type with a large central pith and multiple alternating xylem/pholem groups

typical monocot roots

broad supporting rootsath the bases of some tropical trees

buttress roots

upward-projecting respiratory roots common in waterlogged habitats

pneumatophores

mutualistic fungal association that improves root mineral uptake, especially phosphorus

mycorrhiza

Legume root structure housing nitrogen-fixing bacteria such as Rhizobium

root nodules

supporting roots that descend from stems or branches

prop roots

adventitious supporting roots growing diagonally from lower stem nodes as in maize

stilt roots

roots that contract to pull bulbs or corms deeper into soil

contractile roots

structures of parasitic plants that penetrate a host to absorb resources

Haustoria

Single-cell projections of root epidermis that increase absorptive area

root hairs

ground-tissue region between root epidermis and endodermis

cortex

innermost cortical layer regulating entry into the root stele

Endodermis

Suberized band that interrupts apoplastic flow through root endodermis

Casparian strip

Cell layer just inside the endodermis that gives rise to lateral roots

Pericycle

Central root region containing xylem and phloem

Stele (vascular cylinder)

thin-walled endodermal cells facilitating passage into the stele in some monocot roots

passage cells

movement pathway along cell walls and intercellular spaces

apoplast

movement pathway along cell walls and intercellular spaces

symplast

root xylem maturation pattern: protaoxylem outside, metaxylem inside

exarch

water-resistant polymer deposited in the casparian strip

suberin

young root type commonly showing central star-shaped xylem and little or no pith

typical dicot root

Embryonic root that normally emerges first at germination

Radicle

Prominent main root with smaller later branches, typical of many dicots

Taproot system

Many similarly sized roots, commonly adventitious, typical of many monocots

Fibrous root system

Roots that arise from stems or other organs rather than the embryonic roots

adventitious roots

root branches arising directly from the primary or main root axis

First-order lateral roots

Protective structure over the delicate growing root apex

root cap

starch-containing gravity-sensing bodies in root-cap cells

statoliths

root-tip zone where mitosis produces new cells

region of cell division

root-tip zone where cells mainly lengthen

region of elongation

root-tip where root hairs appear and tissues specialize

region of maturation