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palisade mesophyll (pal-uh-sayd' mez'uh-fil) mesophyll having one or more relatively uniform rows of tightly packed, elongate, columnar parenchyma (chlorenchyma) cells beneath the upper epidermis of a leaf (p. 115) palmately compound; palmately veined (pahl'mayt-lee kom'pownd; pahl'mayt-lee vaynd) having leaflets or principal veins radiating out from a common point (p. 110, 112)

1. Ribosomes, which are considered organelles, are an exception in that they are not bounded by a membrane.

606 Glossary papilla (pl. papillae) (puh-pil'uh; pl. puh-pill'ay) a small, usually rounded or conical protuberance (p. 331) parenchyma (puh-ren'kuh-muh) thin-walled cells varying in size, shape, and function; the most common type of plant cell (p. 55) parental type (pah-renn'tuhl typ) an offspring with the same combination of alleles as one of its parents (p. 249) parthenocarpic (par-thuh-noh-kar'pik) developing fruits from unfertilized ovaries; the resulting fruit is, therefore, usually seedless (p. 448) particle gun (pahrt'ik-kuhl gunn) a machine capable of changing the genetic makeup of plant tissue by shooting DNA-coated particles into it (p. 260) passage cell (pas'ij sel) a thin-walled cell of an endodermis (p. 70) pectin (pek'tin) a water-soluble organic compound occurring primarily in the middle lamella; when combined with organic acids and sugar, it becomes a jelly (p. 35) pedicel (ped'i-sel) the individual stalk of a flower that is part of an inflorescence (p. 132)

peduncle (pee'dun-kul) the stalk of a solitary flower or the main stalk of an inflorescence (p. 132) peptide bond (pep'tyd bond) the type of chemical bond formed when two amino acids link together in the synthesis of proteins (p. 24) perennial (puh-ren'ee-ul) a plant that continues to live indefinitely after flowering (p. 132) perianth (pari'ee-anth) the calyx and corolla of a flower (p. 132) pericarp (per'uh-karp) collective term for all the layers of a fruit wall (p. 136) pericycle (per'uh-sy-kul) tissue sandwiched between the endodermis and phloem of a root; often only one or two cells wide in transverse section; the site of origin of lateral roots (p. 71) periderm (pair'uh-durm) outer bark; composed primarily of cork cells (p. 62) perigynous (purr-idj'uh-nuss) having flower parts attached around the ovary; the flower parts are usually attached to a cup (p. 449) peristome (per'uh-stohm) one or two series of flattened, often ornamented structures (teeth) arranged around the margin of the open end of a moss sporangium; the teeth are sensitive to changes in humidity and facilitate the release of spores (p. 391) petal (pet'ul) a unit of a corolla; it is usually both flattened and colored (p. 132) petiole (pet'ee-ohl) the stalk of a leaf (p. 87, 110)

Pfar-red, or Pfr (pee-far-red or pee-ef-ahr) a form of phytochrome (which see) (p. 215)

pH (pee-aitch) a symbol of hydrogen ion concentration indicating the degree of acidity or alkalinity (p. 82) phage (fayj) see bacteriophage phellogen (fel'uh-jun) see cork cambium phenotype (fee'noh-typ) the physical appearance of an organism (p. 242) pheromone (fer'uh-mohn) something produced by an organism that facilitates chemical communication with another organism (p. 544) phloem (flohm) the food-conducting tissue of a vascular plant (p. 59) photon (foh'ton) a unit of light energy (p. 177)

photoperiodism (foh-toh-pir'ee-ud-izm) the initiation of flowering and certain vegetative activities of plants in response to relative lengths of day and night (p. 214) photosynthesis (foh-toh-sin'thuh-sis) the conversion of light energy to chemical energy; water, carbon dioxide, and chlorophyll are all essential to the process, which ultimately produces carbohydrate, with oxygen being released as a by-product (p. 14, 171) photosynthetic unit (foh-toh-sin-thet'ik yew'nit) one of two groups of about 250 to 400 pigment molecules each that function together in chloroplasts in the light reactions of photosynthesis; the units are exceedingly numerous in each chloroplast (p. 176) photosystem (foh'toh-sis-tum) collective term for a specific functional aggregation of photosynthetic units (p. 178) phragmoplast (frag'mo-plast) a complex of microtubules and endoplasmic retic-ulum that develops during telophase of mitosis (p. 50) phytochrome (fy'tuh-krohm) protein pigment associated with the absorption of light; it is found in the cytoplasm of cells of green plants and occurs in interconvertible active and inactive forms (Pfar red and Pred); it facilitates a plant's capacity to detect the presence (or absence) and duration of light (p. 215) pilus (pl. pili) (py'lis; pl. py'lee) the equivalent of a conjugation tube in bacteria (p. 302)

pinna (pl. pinnae) (pin'uh; pl. pin'ee) a primary subdivision of a fern frond; the term is also applied to a leaflet of a compound leaf (p. 410) pinnately compound; pinnately veined (pin'ayt-lee kom'pownd; pin'ayt-lee vaynd) having leaflets or veins on both sides of a common axis (e.g., rachis, midrib) to which they are attached (p. 110, 112)

pistil (pis'tul) a female reproductive structure of a flower, composed of one or more carpels and consisting of an ovary, style, and stigma (p. 133) pit (pit) a more or less round or elliptical thin area in a cell wall; pits occur in pairs opposite each other, with or without shallow, domelike borders (p. 59)

pith (pith) central tissue of a dicot stem and certain roots; it usually consists of parenchyma cells that become proportionately less of the volume of woody plants as cambial activity increases the organ's girth (p. 88) plankton (plankton) free-floating aquatic organisms that are mostly microscopic (p. 327)

plant anatomy (plant uh-nat uh-mee) the botanical discipline that pertains to the internal structure of plants (p. 8) plant community (plant kuh-myu nuh-tee) an association of plants inhabiting a common environment and interacting with one another (p. 490) plant ecology (plant ee-koll'uh-jee) the science that deals with the relationships and interactions between plants and their environment (p. 9) plant geography (plant jee-og ruh-fee) the botanical discipline that pertains to the broader aspects of the space relations of plants and their distribution over the surface of the earth (p. 9) plant morphology (plant mor-fol uh-jee) the botanical discipline that pertains to plant form and development (p. 9) plant physiology (plant fiz-ee-ol uh-jee) the botanical discipline that pertains to the metabolic activities and processes of plants (p. 8) plant taxonomy (plant tak-son uh-mee) the botanical discipline that pertains to the classification, naming, and identification of plants (p. 9) plasma membrane (plaz muh mem brayn) the outer boundary of the protoplasm of a cell; also called cell membrane, particularly in animal cells (p. 36) plasmid (plaz'mid) one of up to 30 or 40 small, circular DNA molecules usually present in a bacterial cell (p. 260) plasmodesma (pl. plasmodesmata) (plaz-muh-dez' muh; pl. plaz-muh-dez' muh-tah) minute strands of cytoplasm that extend between adjacent cells through pores in the walls (p. 35) plasmodium (pl. plasmodia) (plaz-moh dee-um; pl. plaz-moh'dee-ah) the multinucleate, semiviscous liquid, active form of slime mold; it moves in a "crawling-flowing" motion (p. 348)

plasmolysis (plaz-mol uh-sis) the shrinking in volume of the protoplasm of a

Glossary cell and the separation of the protoplasm from the cell wall due to loss of water via osmosis (p. 157) plastid (plas'tid) an organelle associated primarily with the storage or manufacture of carbohydrates (e.g., leucoplast, chloroplast) (p. 40) plumule (ploo'myool) the terminal bud of the embryo of a seed plant (p. 147) pneumatophore (noo-mat'oh-for) spongy root extending above the surface of the water, produced by a plant growing in water; pneumatophores facilitate oxygen absorption (p. 73) pole (pohl) an invisible focal point toward each end of a cell from which spindle fibers extend in arcs during mitosis or meiosis (p. 224) pollen grain (pahl'un grayn) a structure derived from the microspore of seed plants that develops into a male game-tophyte (p. 133, 425, 444) pollen tube (pahl'un t(y)oob) a tube that develops from a pollen grain and conveys the sperms to the female gameto-phyte (p. 426, 447) pollination (pahl-uh-nay'shun) the transfer of pollen from an anther to a stigma (p. 447)

pollinium (pl. pollinia) (pah-lin'ee-um; pl. pah-lin'ee-ah) a cohesive mass of pollen grains commonly found in members of the Orchid Family (Orchidaceae) and the Milkweed Family (Asclepiadaceae) (p. 453)

polymer (pahl'i-mur) a large molecule composed of many monomers (p. 21) polymerase (poh-limm'err-ace) an enzyme that creates a polymer (e.g., DNA polymerase synthesizes DNA) (p. 234)

polypeptide (pahl-ee-pep'tide) a chain of amino acids (p. 23) polyploidy (pahl'i-ploy-dee) having more than two complete sets of chromosomes per cell (p. 282) pome (pohm) a simple fleshy fruit whose flesh is derived primarily from the receptacle (p. 138) population (pop-yew-lay'shun) a group of organisms, usually of the same species, occupying a given area at the same time (p. 490)

Pred or Pr (pee-red or pee-ahr) a form of phytochrome (which see) (p. 215) pressure-flow hypothesis (presh'ur floh hy-poth'uh-sis) the theory that food substances in solution in plants flow along concentration gradients between the sources of the food and sinks (places where the food is utilized) (p. 165)

prickle (prik'uhl) a pointed outgrowth from an epidermis or cortex beneath the epidermis (p. 119)

primary consumer (pry'mer-ree kon-soo'mur) organism that feeds directly on producers (p. 492) primary tissue (pry'mer-ee tish'yu) a tissue produced by an apical meristem (e.g., epidermis, cortex, primary xylem and phloem, pith) (p. 54) primordium (pry-mord'ee-um) an organ or structure (e.g., leaf, bud) at its earliest stage of development (p. 88) procambium (proh-kam'bee-um) a tissue produced by the primary meristem that differentiates into primary xylem and phloem (p. 54, 68, 88) producer (pruh-dew'sur) an organism that manufactures food through the process of photosynthesis (p. 492) prokaryotic (proh-kair-ee-ot'ik) having a cell or cells that lack a distinct nucleus and other membrane-bound organelles (e.g., bacteria) (p. 32) promoter region (proh-moh'turr ree'jin) the DNA sequence to which RNA poly-merase binds to initiate transcription (p. 237)

proplastid (proh-plas'tid) a tiny, undiffer-entiated organelle that can duplicate itself and that may develop into a chloroplast, leucoplast, or other type of plastid (p. 42) protein (proh'tee-in or proh'teen) a polymer composed of many amino acids linked together by peptide bonds (p. 23)

protein sequencer (proh'tee-in or proh' teen see'kwens-urr) a machine that reveals the sequence of amino acids in a protein (p. 260) prothallus (pl. prothalli) (proh-thal'us; pl. proh-thal'eye) the gametophyte of ferns and their relatives; also called prothallium (p. 412, 413) protoderm (proh'tuh-durm) the primary meristem that gives rise to the epidermis (p. 54, 68, 88) proton (proh'ton) a positively charged particle in the nucleus of an atom (p. 15)

protonema (proh-tuh-nee'muh) a green, usually branched, threadlike or sometimes platelike growth from a bryophyte spore; it gives rise to "leafy" gametophytes (p. 388) protoplast (proh'toh-plast) the unit of protoplasm within a plant cell wall (p. 259) protoplast fusion (proh'toh-plast few'szhinn) the process of combining in vitro two protoplasts in one cell (p. 259) pruning (proon'ing) removal of portions of plants for aesthetic purposes, for improving quality and size of fruits or flowers, or for elimination of diseased tissues (p. 594) pyrenoid (py'ruh-noyd) a small body found on the chloroplasts of certain green algae and hornworts; pyrenoids are associated with starch accumulation; they may occur singly on a chloro-plast, or they may be numerous (p. 328) pyruvic acid (py-roo'vik as'id) the organic compound that is the end product of the glycolysis phase of respiration (p. 186)

quantitative trait (kwan'tuh-tay-tiv trait) a trait controlled by several genes and influenced by the environment; it is usually measured on a continuous scale (p. 248)

quiescence (kwy'ess-ens) a state in which a seed or other plant part will not germinate or grow unless environmental conditions normally required for growth are present (p. 217)

r rachis (ray'kiss) the axis of a pinnately compound leaf or frond extending between the lowermost leaflets or pinnae and the terminal leaflet or pinna (corresponds with the midrib of a simple leaf) (p. 110) radicle (rad'i-kuhl) the part of an embryo in a seed that develops into a root (p. 66, 148) ray (ray) radially oriented tiers of parenchyma cells that conduct food, water, and other materials laterally in the stems and roots of woody plants; they are generally continuous across the vascular cambium between the xylem and the phloem; the portion within the wood is called a xylem ray, while the extension of the same ray in the phloem is called a phloem ray (p. 59) receptacle (ree-sep'tuh-kuhl) the commonly expanded tip of a peduncle or pedicel to which the various parts of a flower (e.g., calyx, corolla) are attached (p. 132)

recessive (ree-ses'iv) a condition in which the phenotypic expression of one allele of a gene is masked by the phenotypic expression of another (dominant) allele (p. 242)

recombinant DNA (ree-komm'bin-int dee-en-ay) a molecule created in vitro containing DNA from at least two organisms (p. 259) recombinant type (ree-komm'bin-int typ) an individual offspring that due to recombination has a combination of alleles different from either of its parents (p. 249)

608 Glossary red tide (red tyd) the marine phenomenon that results in the water becoming temporarily tinged with red due to the sudden proliferation of certain dinoflagellates that produce substances poisonous to animal life and humans (p. 342) reproduction (ree-proh-duk'shun) the development of new individual organisms through either sexual or asexual means (p. 13) resin canal (rez'in kuh-nal') a tubular duct of many conifers and some angio-sperms that is lined with resin-secreting cells (p. 422) respiration (res-puh-ray'shun) the cellular breakdown of sugar and other foods, accompanied by release of energy; in aerobic respiration, oxygen is utilized (p. 14, 171, 186, 189) restriction enzyme (ruh-strikt'shunn en'zym) an enzyme capable of severing a DNA molecule at a specific site (p. 260)

rhizoid (ry'zoyd) a delicate root- or root-hair-like structure of algae, fungi, the gametophytes of bryophytes, and certain structures of a few vascular plants; functions in anchorage and absorption but have no xylem or phloem (p. 357) rhizome (ry'zohm) an underground stem, usually horizontally oriented, that may be superficially rootlike in appearance but that has definite nodes and internodes (p. 100) ribosome (ry'boh-sohm) a granular particle composed of two subunits consisting of RNA and proteins; ribosomes lack membranes, are the sites of protein synthesis, and are very numerous in living cells (p. 40, 237) RNA (ar-en-ay) the standard abbreviation for ribonucleic acid, an important cellular molecule that occurs in three forms, all involved in communication between the nucleus and the cytoplasm and in the synthesis of proteins (p. 26) root (root) a plant organ that functions in anchorage and absorption; most roots are produced below ground (p. 54) root cap (root kap) a thimble-shaped mass of cells at the tip of a growing root; functions primarily in protection (p. 67)

root hair (root hair) a delicate protuberance that is part of an epidermal cell of a root; root hairs occur in a zone behind the growing tip (p. 68) root nodule (root nodd'yewl) a small swelling associated with nitrogen-fixing bacteria that invade the roots of leguminous plants and alders (p. 78) runner (run'ur) a stem that grows horizontally along the surface of the ground;

typically has long internodes; see also stolon (p. 100)

s salt (salt) a substance produced by the bonding of ions that remain after hydrogen and hydroxyl ions of an acid and a base combine to form water (p. 19)

samara (sah-mair'uh) a dry fruit whose pericarp extends around the seed in the form of a wing (p. 142) saprobe (sap'rohb) an organism that obtains its food directly from nonliving organic matter (p. 304) sapwood (sap'wood) outer layers of wood that transport water and minerals in a tree trunk; sapwood is usually lighter in color than heartwood (p. 94) schizocarp (skit'soh-karp) a twin fruit unique to the Parsley Family (Apiaceae) (p. 142)

science (sy'ints) a branch of study involved with the systematic observation, recording, organization, and classification of facts from which natural laws are derived and used predictively (p. 7) scion (sy'un) a segment of plant that is grafted onto a stock (p. 268) sclereid (sklair'id) a sclerenchyma cell that usually has one axis not conspicuously longer than the other; it may vary in shape and is heavily lignified (p. 55)

sclerenchyma (skluh-ren'kuh-muh) tissue composed of lignified cells with thick walls; the tissue functions primarily in strengthening and support (p. 55) secondary consumer (sek'on-dair-ee kon-soo'mer) an organism that feeds on other consumers (p. 492) secondary tissue (sek'un-der-ee tish'yu) a tissue produced by the vascular cambium or the cork cambium (e.g., virtually all the xylem and phloem in a tree trunk) (p. 68) secretory cell, tissue (see'kruh-tor-ee sel, tish'yu) cell or tissue producing a substance or substances that are moved outside the cells (p. 63) seed (seed) a mature ovule containing an embryo and bound by a protective seed coat (p. 133, 222) seed coat (seed' koht) the outer boundary layer of a seed; it is developed from the integument(s) (p. 422, 426, 443) semiconservative replication (semm'ee-kon-surv-uh-tiv repp-lee-kay'shun) DNA replication mechanism that ensures each daughter molecule has one parental strand and one new strand (p. 234)

semipermeable membrane (sem-ee-pur'-me-uh-bil mem-brayn) see differentially permeable membrane senescence (suh-ness'ints) the breakdown of cell components and membranes that leads to the death of the cell (p. 205) sepal (see'puhl) a unit of the calyx that frequently resembles a reduced leaf; sepals often function in protecting the unopened flower bud (p. 132) sessile (sess'uhl) without petiole or pedicel;

attached directly by the base (p. 110) seta (see'tuh) the stalk of a bryophyte sporophyte (p. 386) sexual reproduction (seksh'yule ree-proh-duk'shun) reproduction involving the union of gametes (p. 222) short-day plant (short-day plant) a plant in which flowering is initiated when the days are shorter than its critical photoperiod (p. 214) sieve plate (siv playt) an area of the wall of a sieve tube member that contains several to many perforations that permit cytoplasmic connections between similar adjacent cells, the cytoplasmic strands being larger than plasmodesmata (p. 60) sieve tube (siv t(y)oob) a column of sieve-tube members arranged end to end; food is conducted from cell to cell through sieve plates (p. 60) sieve tube member (siv t(y)oob mem'bur)

a single cell of a sieve tube (p. 60) silique (suh-leek') a dry fruit that splits along two "seams," with the seeds borne on a central partition (p. 138) simple fruit (sim'pul froot) a fruit that develops from a single pistil (p. 136) simple leaf (sim'pul leef) a leaf with the blade undivided into leaflets (p. 110) slime mold (slym mold) a simple organism that moves like an amoeba but resembles a fungus when reproducing (p. 348)

solvent (sol'vent) a substance (usually liquid) capable of dissolving another substance (p. 156) somatic hybrid (soh-matt'ik hy'brid) a plant produced by protoplast fusion (p. 259)

somatic mutation (soh-matt'ik mew-tay'shun) a mutation in a somatic (body) cell; such a mutation is not passed on to offspring (p. 238) sorus (pl. sori) (sor'uss; pl. sor'eye) a cluster of sporangia; the term is most frequently applied to clusters of fern sporangia (p. 411) speciation (spee-see-ay'shun) the origin of new species through evolution (p. 239) species (spee'seez; species is spelled and pronounced the same way in either singular or plural form; there is no such thing as a specie) the basic unit

Glossary of classification; a population of individuals capable of interbreeding freely with one another but because of geographic, reproductive, or other barriers, do not in nature interbreed with members of other species (p. 288) sperm (spurm) a male gamete; except for those of red algae and angiosperms, sperms are frequently motile and are usually smaller than the corresponding female gametes (p. 222, 332, 426) spice (spyss) an aromatic organic plant product used to season or flavor food or drink (p. 571) spindle (spin' duhl) an aggregation of fiberlike threads (microtubules) that appears in cells during mitosis and meiosis; some threads are attached to the centromeres of chromosomes, whereas other threads extend directly or in arcs between two invisible points designated as poles (p. 48, 49) spine (spyn) a relatively strong, sharp-pointed, woody structure usually located on a stem; it is usually a modified leaf or stipule (p. 119) spongy mesophyll (spun jee mez uh-fil) mesophyll having loosely arranged cells and numerous air spaces; it is generally confined to the lower part of the interior of a leaf just above the lower epidermis (p. 115) sporangiophore (spuh-ran jee-uh-for) the stalk on which a sporangium is produced (p. 358) sporangium (pl. sporangia) (spuh-ran'jee-um; pl. spuh-ran'jee-uh) a structure in which spores are produced; it may be either unicellular or multicellular (p. 349, 358, 382) spore (spor) a reproductive cell or aggregation of cells capable of developing directly into a gametophyte or other body without uniting with another cell (Note: a bacterial spore is not a reproductive cell but is an inactive phase that enables the cell to survive under adverse conditions); sexual spores formed as a result of meiosis are often called meiospores; spores produced by mitosis may be referred to as vegetative spores (p. 227, 349, 358) sporocyte (spor oh-site) a diploid cell that becomes four haploid spores or nuclei as a result of undergoing meiosis (p. 227, 387) sporophyll (spor uh-fil) a modified leaf that bears a sporangium or sporangia (p. 400)

sporophyte (spor uh-fyt) the diploid (2n) spore-producing phase of the life cycle of an organism exhibiting Alternation of Generations (p. 227) stamen (stay min) a pollen-producing structure of a flower; it consists of an anther and usually also a filament (p. 133)

stele (steel) the central cylinder of tissues in a stem or root; usually consists primarily of xylem and phloem (p. 90) stem (stem) a plant axis with leaves or ena-

tions (p. 54) stigma (stig muh) the pollen receptive area of a pistil (p. 133) stipe (styp) the supporting stalk of seaweeds, mushrooms, and certain other stationary organisms (p. 337) stipule (stip'yool) one of a pair of appendages of varying size, shape, and texture present at the base of the leaves of some plants (p. 87) stock (stok) the rooted portion of a plant to which a scion is grafted (p. 268) stolon (stoh lun) a stem that grows vertically below the surface of the ground; it typically has relatively long internodes; see also runner (p. 100) stoma (pl. stomata) (stoh'muh; pl. stoh mah-tuh) a minute pore or opening in the epidermis of leaves, herbaceous stems, and the sporophytes of hornworts (Anthoceros); it is flanked by two guard cells that regulate its opening and closing and thus regulate gas exchange and transpiration (p. 61, 113) strobilus (pl. strobili) (stroh'buh-luss; pl. stroh buh-leye) an aggregation of sporophylls on a common axis; it usually resembles a cone or is somewhat conelike in appearance (p. 400, 407) stroma (stroh muh) a region constituting the bulk of the volume of a chloroplast or other plastid; it contains enzymes that in chloroplasts play a key role in carbon fixation, carbohydrate synthesis, and other photosynthetic reactions (p. 40)

style (styl) the structure that connects a stigma and an ovary (p. 133) subculture (subb kull-choor) the transfer of tissue culture plantlets or plant parts to a new medium, usually as a form of propagation (p. 270) suberin (soo buh-rin) a fatty substance found primarily in the cell walls of cork and the Casparian strips of endodermal cells (p. 62, 90) succession (suk-sesh un) an orderly progression of changes in the composition of a community from the initial development of vegetation to the establishment of a climax community (p. 498)

sucrose (soo'krohs) a disaccharide composed of glucose and fructose; the primary form in which sugar produced by photosynthesis is transported throughout a plant (p. 21)

superior ovary (soo-peer ee-or oh vuh-ree) an ovary that is free from the calyx, corolla, and other floral parts, so the sepals and petals appear to be attached at its base (p. 133, 449) symbiosis (sim-by-oh siss) an intimate association between two dissimilar organisms that benefits both of them (mutualism) or is harmful to one of them (parasitism) (p. 300) syngamy (sin ' gam-mee) a union of gametes; fertilization (p. 228)

2n (too-en) having two sets of chromosomes; diploid (p. 227) 3n (three-en) having three sets of chromosomes; triploid (p. 227, 447) tendril (ten dril) a slender structure that coils on contact with a support of suitable diameter; it usually is a modified leaf or leaflet and aids the plant in climbing (p. 103, 118) thallus (pl. thalli) (thal'uss; pl. thal'eye) a multicellular plant body that is usually flattened and not organized into roots, stems, or leaves (p. 337, 375, 385)

thorn (thorn) a pointed specialized stem (p. 119)

thylakoid (thy luh-koyd) coin-shaped membranes whose contents include chlorophyll; they are arranged in stacks that form the grana of chloroplasts (p. 41) tip layering (tipp lay urr-ing) asexual propagation involving the burying of the tip of a flexible stem in soil to induce the formation of adventitious roots; the rooted portion is then cut from the parent plant and grown separately (p. 267) tissue (tish'yu) an aggregation of cells having a common function (p. 54) tissue culture (tish yu kul chur) the culture of isolated living tissue on an artificial medium (p. 269) totipotency (toh-tuh-poh ten-see) the potential of a cell to develop into a complete plant (p. 269) tracheid (tray kee-id) a xylem cell that is tapered at the ends and has thick walls containing pits (p. 59) transcript (tran'skriptt) the RNA molecule formed by transcription (p. 237) transcription (trans-krip shun) the copying of a sequence of DNA nucleotides into an RNA sequence (p. 236)

transformation (trans-forr-may shun) the transfer of DNA from one organism to another (p. 260)

610 Glossary transgenic plant (trans-jeen'ik plant) a plant containing recombinant DNA (p. 259) translation (trans-lay'shun) the process of decoding RNAinto protein (p. 237) translocation (trans-loh-kay'shun) a chromosomal rearrangement resulting from a segment of one chromosome being moved to another chromosome (p. 240)

transpiration (trans-puh-ray'shun) loss of water in vapor form; most transpiration takes place through the stomata (p. 110, 266)

transposable genetic element (trans-poh'suh-bil juh-nett'ik el'uh-mint) a DNA sequence (transposon) capable of being moved from one chromosomal location to another (p. 231) transposition (trans-poh-zish'unn) the movement of a transposable genetic element (p. 231) tropism (troh'pizm) response of a plant organ or part to an external stimulus, usually in the direction of the stimulus (p. 207)

tuber (t(y)oo'bur) a swollen, fleshy underground stem (e.g., white potato) (p. 100)

turgid (tur'jid) firm or swollen because of internal water pressures resulting from osmosis (p. 157) turgor movement (turr'gor moov'mint) the movement that results from changes in internal water pressures in a plant part (p. 210) turgor pressure (tur'gur presh'ur) pressure within a cell resulting from the uptake of water (p. 157)

u unisexual (yu-nih-seksh'yu-ul) a term usually applied to a flower lacking either stamens or a pistil (p. 450)

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