Glossary A of on other roots, buds developing on leaves or roots abaxial Directed away from the axis. Opposite of instead of in leaf axils on shoots. adaxial. With regard to a leaf, the lower, or “dorsal,” aerenchyma Parenchyma tissue containing particu- surface. larly large intercellular spaces of schizogenous, lysige- accessory bud A bud located above or on either side nous, or rhexigenous origin. of the main axillary bud. aggregate ray In secondary vascular tissues; a group accessory cell See subsidiary cell. of small rays arranged so as to appear to be one large acicular crystal Needle-shaped crystal. ray. acropetal development (or differentiation) Pro- albuminous cell See Strasburger cell. duced or becoming differentiated in a succession toward aleurone Granules of protein (aleurone grains) the apex of an organ. The opposite of basipetal but present in seeds, usually restricted to the outermost means the same as basifugal. layer, the aleurone layer of the endosperm. (Protein actin fi lament A helical protein fi lament, 5 to 7 nano- bodies is the preferred term for aleurone grains.) meters (nm) thick, composed of globular actin mole- aleurone layer Outermost layer of endosperm in cules; a major constituent of all eukaryotic cells. Also cereals and many other taxa that contains protein bodies called microfi lament. and enzymes concerned with endosperm digestion. actinocytic stoma Stoma surrounded by a circle of aliform paratracheal parenchyma In secondary radiating cells. xylem; vasicentric groups of axial parenchyma cells adaxial Directed toward the axis. Opposite of having tangential wing-like extensions as seen in trans- abaxial. With regard to a leaf, the upper, or “ventral,” verse section. See also paratracheal parenchyma and surface. vasicentric paratracheal parenchyma. adventitious Refers to structures arising not at their alternate pitting In tracheary elements; pits in diago- usual sites, as roots originating on stems or leaves instead nal rows. Esau’s Plant Anatomy, Third Edition, By Ray F. Evert. Copyright © 2006 John Wiley & Sons, Inc. 521 522 | Glossary amyloplast A colorless plastid (leucoplast) that forms precursors of the primary tissues of root or shoot; may starch grains. be vegetative, initiating vegetative tissues and organs, anastomosis Refers to cells or strands of cells that are or reproductive, initiating reproductive tissues and interconnected with one another as, for example, the organs. veins in a leaf. apoplast Cell wall continuum and intercellular spaces analogy Means having the same function as but a dif- of a plant or plant organ; the movement of substances ferent phylogenetic origin than another entity. via the cell walls is called apoplastic movement or anatomy The study of the internal structure of transport. organisms; morphology is the study of their external apoptosis Programmed cell death in animal cells structure. mediated by a group of protein-degrading enzymes angiosperm A group of plants whose seeds are borne called caspases; involves a programmed series of events within a mature ovary (fruit). that leads to dismantling of the cell contents. angstrom (originally ångström) A unit of length apotracheal parenchyma In secondary xylem; axial equal to one-tenth of a nanometer (nm). Symbol A or parenchyma typically independent of the vessels (pores). Å. Includes diffuse and diffuse-in-aggregates. angular collenchyma A form of collenchyma in apposition Growth of cell wall by successive deposi- which the primary wall thickening is most prominent tion of wall material, layer upon layer. Opposite of in the angles where several cells are joined. intussusception. anisocytic stoma A stomatal complex in which three articulated laticifer Laticifer composed of more than subsidiary cells, one distinctly smaller than the other one cell with common walls intact or partly or entirely two, surround the stoma. removed; anastomosing or nonanastomosing; a com- anisotropic Having different properties along differ- pound laticifer. ent axes; optical anisotropy causes polarization and aspirated pit In gymnosperm wood; bordered pit in double refraction of light. which the pit membrane is laterally displaced and the annual ring In secondary xylem; growth ring formed torus blocks the aperture. during one season. The term is deprecated because astrosclereid A branched, or ramifi ed, type of more than one growth ring may be formed during a sclereid. single year. axial organ Root, stem, infl orescence, or fl ower axis annular cell wall thickening In tracheary elements without its appendages. of the xylem; secondary wall deposited in the form of axial parenchyma Parenchyma cells in the axial rings. system of secondary vascular tissues; as contrasted with anomalous secondary growth A term of conve- ray parenchyma cells. nience referring to types of secondary growth that axial system All secondary vascular cells derived differ from the more familiar ones. from the fusiform cambial initials and oriented with anomocytic stoma A stoma without subsidiary their longest diameter parallel with the main axis of cells. stem or root. Other terms: vertical system and longitu- anther Pollen-bearing part of the stamen. dinal system. anthocyanin A water-soluble blue, purple, or red fl a- axial tracheid Tracheid in the axial system of second- vonoid pigment occurring in the vacuolar cell sap. ary xylem; as contrasted with ray tracheid. Anthophyta The phylum of angiosperms, or fl ower- axil Upper angle between a stem and a twig or a ing plants. leaf. anticlinal Commonly refers to orientation of cell wall axillary bud Bud in the axil of a leaf. or plane of cell division; perpendicular to the nearest axillary meristem Meristem located in the axil of a surface. Opposite of periclinal. leaf and giving rise to an axillary bud. apex (pl. apices), or summit Tip, topmost part, pointed end of anything. In shoot or root the tip con- B taining the apical meristem. banded parenchyma In secondary xylem; axial apical cell Single cell that occupies the distal position parenchyma in concentric bands as seen in transverse in an apical meristem of root or shoot and is usually section, mainly independent (apotracheal) of vessels interpreted as the initial cell in the apical meristem; (pores). typical of seedless vascular plants. bark A nontechnical term applied to all tissues outside apical dominance Infl uence exerted by a terminal the vascular cambium or the xylem; in older trees bud in suppressing the growth of lateral, or axillary, may be divided into dead outer bark and living inner buds. bark, which consists of secondary phloem. See also apical meristem A group of meristematic cells at the rhytidome. apex of root or shoot that by cell division produces the bars of Sanio See crassulae. Glossary | 523 basifugal development See acropetal development. callus A tissue composed of large thin-walled cells basipetal development (or differentiation) Pro- developing as a result of injury, as in wound healing duced or becoming differentiated in a succession toward or grafting, and in tissue culture. (The use of callus the base of an organ. The opposite of acropetal and for accumulations of callose on sieve areas is basifugal. deprecated.) bast fi ber Originally phloem fi ber, now any extraxyl- callus tissue See callus. ary fi ber. calyptrogen In root apex; meristem giving rise to the bicollateral vascular bundle A bundle having rootcap independently of the initials of cortex and phloem on two sides of the xylem. central cylinder. biseriate ray A ray in secondary vascular tissue, two cambial initials Cells so localized in the vascular cells in width. cambium or phellogen that their periclinal divisions can blind pit A pit without a complementary pit in an contribute cells either to the outside or to the inside of adjacent wall, which may face a lumen of a cell or an the axis; in vascular cambium, classifi ed into fusiform intercellular space. initials (source of axial cells of xylem and phloem) and bordered pit A pit in which the secondary wall over- ray initials (source of the ray cells). arches the pit membrane. cambium A meristem with products of periclinal bordered pit-pair An intercellular pairing of bor- divisions commonly contributed in two directions and dered pits. arranged in radial fi les. Term preferably applied only to boundary parenchyma See marginal bands. the two lateral meristems, the vascular cambium and brachysclereid A short, roughly isodiametric scler- the cork cambium, or phellogen. eid, resembling a parenchyma cell in shape; a stone Casparian strip, or band A band-like wall formation cell. within primary walls that contains suberin and lignin; branch gap In the nodal region of a stem; a region of typical of endodermal cells in roots, in which it occurs parenchyma in the vascular cylinder of the stem located in radial and transverse anticlinal walls. where the branch traces are bent toward the branch. cell Structural and physiological unit of a living organ- Usually confl uent with the gap of the leaf subtending ism. The plant cell consists of protoplast and cell wall; the branch. in nonliving state, of cell wall only, or cell wall and some branch root See lateral root. nonliving inclusions. branch traces Vascular bundles connecting the vas- cell plate A partition appearing at telophase between cular tissue of the branch and that of the main stem. the two nuclei formed during mitosis (and some meioses) They are leaf traces of the fi rst leaves (prophylls) on the and indicating the early stage of the division of a cell branch. (cytokinesis) by means of a new cell wall; is formed in branched pit See ramiform pit. the phragmoplast. bulliform cell An enlarged epidermal cell present, cell wall More or less rigid outermost layer of plant with other similar cells, in longitudinal rows in leaves cells, which encloses the protoplast. In higher plants, of grasses. Also called motor cell because of its pre- composed of cellulose and other organic and inorganic sumed participation in the mechanism of rolling and substances.