Plant Biology (chapters 8-10)

adventitious roots

Refers to an organ that forms in an unusual place; refers primarily to roots that form on leaves, nodes, or cuttings rather than on another root

buttress roots

A root that grows asymmetrically such that it becomes very tall and thin, extending up the trunk as much as a meter or more and giving the trunk lateral stability

casparian strips

A layer of impermeable lignin and suberin in the walls of endodermal cells, preventing diffusion of material through that portion of the wall

ectomycorrhizal relationship

A type in which the fungi invade only the outermost cells of the root

endodermis

A sheath of cells surrounding the vascular tissue of roots (and occasionally horizontal stems); their Casparian strips prevent uncontrolled diffusion between root cortex and root vascular tissue by means of walls and intercellular spaces

endomycorrhizal association

A type in which the fungi invade all cells of the root cortex

fibrous root system

A set of roots in which all roots are more or less the same size; that is, none is especially larger than any other root (none is a taproot)

haustoria

The structure by which a parasite enters and draws nutrients from a plant; in fungi, it is a hypha; in mistletoes and similar parasites, it is a modified root

lateral roots/branch roots

Any root that is borne by another root (i.e., any root that is not attached to a stem or other nonroot organ)

order of bark growth

cork - cork cambium - 2 phloem - vascular cambium - 2 xylem

mycorrhizae

Fungi that form a symbiotic relationship with roots, usually of benefit to plants because they provide phosphorus

what does the periderm consist of?

cork cambium + layers of cork + any cells to the inside from cork cambium

nitrogen fixation

The conversion of atmospheric nitrogen into any compound that can be used by plants, typically either nitrate or ammonium

pericycle

An irregular band of cells in the root, located between the endodermis and the vascular tissue

prop roots

Any root that grows through air or water before entering soil; prop roots help to brace and stabilize a shoot

quiescent center

Portion of the root apical meristem in which cell division does not occur

radicle

The main root of a seed; it is the direct continuation of the embryonic stem

root apical meristem

The set of cells capable of dividing, located at the apex of a root. Produces the root itself and also the root cap

Root cap

A layer of parenchyma cells that cover and protect the root apex.

root hairs

A short-lived trichome near a root apex. Root hairs increase the surface area and absorptive capacity of roots; being single, slender cells, they enter soil pores that are too small for whole root tips to enter

root nodule

Several species of plants have symbiotic relationships with nitrogen-fixing bacteria; in some species, especially those of legumes, portions of roots become swollen and occupied by the bacteria

taproots

Technically, a taproot is only the root that develops from the radicle (the embryonic root). Very commonly the term “taproot” is used to refer to any root that is markedly larger than most other roots

zone of elongation

Region of a root tip, just proximal to the root apical meristem, where cells undergo pronounced elongation

wood

secondary xylem

vascular cambium

The meristem that produces secondary vascular tissues—secondary xylem (wood) and secondary phloem (inner bark)

tylosis

After a vessel stops conducting because of cavitation, adjacent cells may push cytoplasm into the vessel through pits, plugging the vessel

storied cambium

A vascular cambium in which fusiform initials are aligned horizontally. Alternative: nonstoried cambium

softwoods

A term applied to both gymnosperms and their wood, because few gymnosperms have any fibers in their wood

secondary xylem

Xylem derived from the vascular cambium

secondary vascular bundles

In monocots with anomalous secondary growth (such as Joshua trees), secondary vascular bundles are those produced by the cambial zone.

secondary tissues

The tissues of the secondary plant body-those produced by the vascular cambium and the cork cambium. Alternative: primary tissues.

secondary phloem

Phloem derived from the vascular cambium

sapwood

The light-colored, light-scented outermost wood of a trunk or branch; conduction is still occurring and many wood parenchyma cells are alive. Alternative: heartwood.

ring porous 

Wood in which the early wood has more numerous and larger vessels than the late wood. Alternative: diffuse porous wood

reaction wood

Wood formed in response to mechanical stress. tension wood The reaction wood of eudicots, formed on the upper side of a branch. compression wood The reaction wood of gymnosperms, formed on the lower side of a branch.

rays

In secondary xylem and phloem, a radial series of cells produced by ray initials. Alternative: axial tissue

ray tracheids

Horizontal tracheids in the secondary xylem rays of gymnosperms

ray initials

In a vascular cambium, the short cells that give rise to the rays of the secondary xylem and phloem. Alternative: fusiform initials

radial system

The set of rays within wood

primary tissues

The tissues derived more or less directly from an apical meristem or leaf primordium; the tissues of the primary plant body. Alternative: secondary tissues

phellogen

Synonym for cork cambium

phellem cell

Technical term for cork

periderm

Technical term for bark; it consists of cork, cork cambium, and any enclosed tissues such as secondary phloem

perclinal wall

A wall that is parallel to a nearby surface, especially the outer surface of the plant. Alternative: anticlinal wall

nonstoried cambium 

A cambium in which the fusiform initials are not aligned horizontally. Alternative: storied cambium.

lenticels

In bark, a region of cork cells with intercellular spaces, permitting diffusion of oxygen into inner tissues.

late wood

Synonym for summer wood.

included phloem

In certain types of anomalous secondary growth, patches of secondary phloem may be located within the secondary xylem

heartwood

The colored, aromatic wood in the center of a trunk or branch; all the wood parenchyma cells have died and no water conduction is occurring. Alternative: sapwood

hardwoods

The colored, aromatic wood in the center of a trunk or branch; all the wood parenchyma cells have died and no water conduction is occurring. Alternative: sapwood

growth ring

Synonym for annual ring in wood. “Growth ring” is preferred because rings are occasionally not strictly annual (sometimes two are produced in 1 year, and none might be produced in adverse years).

fusiform initials

In a vascular cambium, the long cells with tapered ends that give rise to axial cells of the secondary xylem and secondary phloem. Alternative: ray initials.

establishment growth

In palms, seedlings initially grow wider while remaining short; during this establishment growth, the seedling establishes additional adventitious roots.

early wood

synonym for spring wood.

diffuse porous

Wood in which the vessels of late wood are about as numerous and as wide as those of early wood. Alternative: ring porous wood.

cork cell

A cell in bark that has walls encrusted with suberin; cork prevents loss of water through the bark and prevents entry of pathogens.

cork cambium

A layer of cells that produces the cork cells of bark. Also called phellogen

bark

In some plants, especially woody, perennial plants, the epidermis is replaced by bark, which always contains at least cork cells produced by cork cambia; bark may also contain secondary phloem, sclereids, and fibers (bast fibers).

axial system

In secondary xylem (wood) and secondary phloem, the axial system consists of the cells derived from fusiform initials; most cells in the axial system (e.g., tracheids, vessel elements, fibers, sieve tube members) are elongate parallel to the long axis of the wood or phloem. Alternative: ray system.

anticlinal walls

A wall perpendicular to a nearby surface, especially the outer surface of the plant. Alternative: periclinal wall.

annual ring

In secondary xylem, the set of wood, usually early wood and late wood, produced in 1 year.