Glossary

A

Abaxial - describing the side of lateral organs facing away from the stem or main axis, i.e. the lower surface. Compare to adaxial.


Adaxial - describing the side of lateral organs facing toward the stem or main axis, i.e. the upper surface. Compare to abaxial.


B

Bicollateral bundle - vascular bundles where primary phloem differentiates not only in the normal exarch position but on the inner edge of primary xylem as well.


C

C3 plant - any plant that produces, as the first step in photosynthesis, phosphoglyceric acid, which contains three carbon atoms.


C4 plant - any plant that produces, as the first step in photosynthesis, oxaloacetic acid, which contains four carbon atoms. See also Kranz anatomy.


Collenchyma - a tissue composed of relatively elongated cells with secondarily thickened walls of cellulose. A supporting or strengthening tissue.


Chlorenchyma - tissue and cells, specialised parenchyma with chloroplasts.


Companion cell - of phloem, a specialised parenchyma cell characterised by a dense cytoplasm and conspicuous nucleus, associated with an adjacent sieve-tube element.


Cortex - the tissue between the epidermis and the stele of stems and roots, consisting of parenchyma and often also collenchyma and/or sclerenchyma and sometimes chlorenchyma.


Cuticle - the continuous layer of cutin secreted by the epidermis, it prevents plant desiccation by being impervious to water and gas exchange and covers the aerial parts of the plant body, broken only by stomata and lenticels.


D

Dicotyledon leaf - defined by the presence of a vascular cambium (which may or may not be active), as well as usually reticulate venation.


Dorsi-ventral - of leaves where the mesophyll is differentiated into an upper and lower layer (palisade and spongy mesophyll), contrasting with iso-bilateral.


E

Endarch - referring to cells differentiating towards the inside of the stem, contrasting with exarch.


Epidermis - the outermost cells of the primary plant body, usually consisting of a single layer but sometimes several layers thick.


Exarch - referring to cells differentiating towards the outside of the stem, contrasting with endarch.


F

Fibre - a relatively long sclerenchyma cell, usually occurring in bundles or strands. See also Sclerenchyma.


H

Hairs - see Trichomes.


I

Iso-bilateral - leaves where the mesophyll is not differentiated into an upper and lower layer, contrasting with dorsi-ventral.


K

Kranz anatomy - Of leaves of C4 plants, where the vascular bundle sheath comprises large cells that often radiate out from the bundle sheath like spokes and contain a greater abundance of often larger chloroplasts than usual cells.

M

Mesophyll - leaf tissue between the upper and lower epidermis, made up of parenchyma cells and often comprising two layers, palisade mesophyll and spongy mesophyll.


Mestome sheath - the inner of 2 rings of cells (the bundle sheath) around the vascular bundle of monocots.


Metaxylem - the latter formed primary xylem, consisting of scalariform, reticulate and pitted vessels.


Monocotyledon leaf - lacks a vascular cambium and usually has parallel venation and the xylem arranged in a U or V shaped pattern in the vascular bundle.


P

Parenchyma - relatively unspecialised ground tissue composed of polyhedral cells with thin non-lignified cellulose cell walls and living protoplasts.


Petiole - the stalk that attaches the leaf lamina to the stem.


Phloem - a vascular tissue whose principal function is the translocation of sugars and other nutrients. Consists of sieve tubes, companion cells, parenchyma and sclerenchyma. See also sieve tubes, sieve plates and companion cells.


Phyllode - a leaf petiole modified for photosynthesis.


Pith - a region of parenchymatous tissue found in the centre of many plant stems and non-woody roots to the inside of the stele.


Primary xylem - xylem derived from the procambium in the primary plant body, consisting of protoxylem) and metaxylem. See also protoxylem and metaxylem. Compare to secondary xylem.


Protoxylem - the first formed primary xylem, consisting of annular and spiral (helical) vessels.


S

Safranin - a histological stain that stains lignified cells red.


Sclerenchyma - strengthening tissue composed of relatively short cells (sclereids) and/or relatively long ones (fibres) with secondarily thickened cell walls of lignin and usually lacking a living protoplast at maturity.


Sclereid - a relatively short sclerenchyma cell, often irregular in shape. See also sclerenchyma.


Secondary growth - new cells and tissues derived from secondary meristems, such as secondary xylem and phloem, leading to an increase in girth.


Secondary thickening - of cells, the deposition of lignin or cellulose onto the primary cell wall to give rise to sclerenchyma and collenchyma cells respectively.


Secondary xylem - xylem derived from the vascular cambium in plants exhibiting secondary growth. Wood is secondary xylem.


Sieve-plates - of sieve tubes, a perforated modification of the end walls between adjacent elongated sieve tube elements. See also sieve-tube.


Sieve tube - of phloem, a continuous longitudinal tube characterised by sieve plates, non-lignified secondary cell walls and a living protoplast.


Slime-plugs - of phloem sieve-tubes, where the sieve-tube contents are deposited at sieve plates and a thin strand extends through the centre of the tube element. Caused by damage to the sieve-tubes.


Stoma - (pl. stomata) specialised pore in the epidermis (usually of leaves and stems) that allow gaseous exchange for photosynthesis and respiration and the transpiration of water vapour to the atmosphere.


Sun/shade leaves - leaves exposed to full sun tend to have thicker cuticles and more layers of palisade tissue than leaves of the same plant growing in shade.


T

Toluidine-blue - a histological stain. Lignified walls stain greenish-blue, bright blue or white. Most primary (non-lignified) walls stain pinkish-purple (e.g. parenchyma).


Trichome - an outgrowth from an epidermis; a hair or scale which may be unicellular or multicellular, branched or unbranched, secretory, absorbing or non-functional.

V

Vascular cambium - a secondary meristem, the cells of which give rise to secondary xylem and phloem, leading to an increase in stem girth.


X

Xylem - vascular tissue whose principal function is the upward translocation of water and solutes; see also primary xylem or secondary xylem.