T

taproot. A root having a prominent central portion growing vertically downward, taxonomy. The study of classification.

teliospore. In rust fungi, a thick-walled spore in which meiosis follows the union of gametic nuclei, telophase. That phase in mitosis following anaphase, when chromosomes arrive at the poles.

template. A pattern upon which another thing is formed. Used here in reference to a molecule, terrestrial. Dwelling on land, test cross. See back cross.

tetrad. A group of four spores formed from a spore mother cell by meiotic divisions.

Tetrasporine. A theoretical line of evolution among the green algae comprising a uniseriate series of uninucleated cells. Presumed to be the ancestral form of the vascular plants, tetrasporophytes. In the life cycle of red algae, spores that are produced by diploid carpospores and reproduce by the production of tetraspores. thallophyte. Member of the phylum Thallophyta. Characterized by a thallus, a plant body lacking specialized conducting tissues and displaying simplicity of form.

thallus. A plant body that lacks specialized conducting tissues, roots, stems, and leaves.

thylakoid. The lamellae of the grana that occur within the chloroplast. torus. A thickened portion of primary wall lying at the center of a pit. totipotency. When all the cells of a body (the somatic cells) have a complete set of genes. If any one of them recovers the capacity to divide, it can result in the formation of a complete individual, tracheid. An elongated, thick-walled, conducting and supporting cell of xylem.

Tracheophyta. The vascular plants.

translocation. A segment of a chromosome breaking away from its parent member and attaching to a different chromosome, transpiration. The loss of water on the part of a plant, trench layering. A vegetative method of plant reproduction wherein a cane or stem is placed in a trench and covered with soil, trichogyne. A receptive emergence from an oogonium and through which spermatia may travel to the egg nucleus. Occurs in both ascomycetes and red algae.

tripeptide. Three amino acids linked by peptide bonds, triplet. A codon. The three bases that represent instruction to use a particular amino acid in the construction of a protein. t-RNA. Transfer RNA. A type of RNA that functions as a carrier molecule to bring amino acids to the ribosomes, where they may then be assembled into polypeptides.

truffle. A subterranean mushroom belonging to the Ascomycetes class, tube nucleus. The one of two nuclei that result when a pollen grain germinates on the stigma of a flower and that then leads down the pollen tube.

tuber. A thick, fleshy terminal part of a stem, usually formed underground, turgor. The state of turgidity, or tension, in living cells. The distension of the protoplasm against the cell wall, caused by the cell's fluid content, turgor pressure. The pressure that develops because of the fluid in a turgid plant cell. Results from water flowing into the cell, tylose. The intrusion of the cytoplasm of one cell into a neighboring cell, resulting in obstruction of the cavity of the second cell.

u ultracentrifugation. Very high-speed centrifugation that makes possible the sedimentation of colloidal and other small particles. Used in the stratification of cell components, ultraviolet. Beyond the visible spectrum at the violet end. Having a wavelength shorter than that of visible light, unicellular. Composed of a single cell, uninucleated. Having a single nucleus, uniseriate. In a single row of cells.

unit characters. One of Gregor Mendel's laws of heredity, which declares that each characteristic is transmitted as a single and unchanging unit, universal veil. Veil that surrounds a mushroom when the mushroom is still in a button stage.

urediniospore. Also called a uredospore. In the red-cell stage of the life cycle of a rust fungus, a one-celled, summer spore, uredospore. See urediniospore.

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