Trophic Level - Refers to the rank of organisms in an ecosystem on the basis of the method by which organisms are deriving their organic food in the food chain and representing a step of energy transfer in the sequence of energy flow through the bioic component of ecosystem.

Trophotropism - A reaction in a growing organ included by the chemical nature of the environment.

Tropic Curvature - A curvature of a plant organ which is caused by onesided growth under the influence of a stimulus falling on the plant from one side.

Tropism - Used for response to a stimulus by a growth curvature, the direction of the curvature being ascertained by the direction from which the stimulus originates.

Tropophyte - Refers to a plant that has been adapted to survive in climate of alternating dry and wet seasons by having a resting phase during dry season.

True Fruit - A fruit which is formed from the ovary.

Truffls - Refers to the members of order Tuberales of Discomycetes. They form underground ascospores which resemble tubers. They include about 35 genera and about 230 species, many of which are edible. Certain species occur under particular trees. e.g., Tuber melanosporum under oaks and are considered to be my corrhizal.

Tube Cell (tube nucleus). Used for one of the cells present in the microspore of gymnosperms. In Cycas, it enters haustorial pollen tube but its function is not known with certainly. In angiosperms the cell at the tip of pollen tube that precedes generative nuclei is sometimes known as tube cell but more often is known as vegetative nucleus.

Tube Germination - Germination of a spore by forming a hypha (germ tube).

Tube Nucleus - Refers to the non - generative nucleus in a pollen - tube. It probably plays some role in regulating the development and behaviour of that organ.

Tuber - A swollen underground stem or root, which contains stored food, and acts as an organ of perennation and vegetative propagation.

Tuberculate (verrucose). Refers to the structure whose surface is covered with small watery projections e.g., rind of ridge cucumber.

Tumour Inducing Principle - Refers to a plasmid carried by bacterium Agrobacterium tumefaciens that causes crown gall disease in plants. Theplasmid is essential for converting normal tissue of host into tumour tissue which involves incorporation of plasmid into the plant genome. It is of interest to note that the tissue removed from crown gall tumours can grow in culture medium without adding auxin and cytokinin.

Tundra - Refers to a cold desert characterized by the scanty xerophytes vegetation in which mosses and lichens are dominant.

Tunica - A coat, especially a thin, membrane which is present round theperidiole in most species of the Nidulariaceae.

Tunica-Corpus Theory - Refers to the theory about organization and development of apical meristem. According to this theory, meristematic region gets differented into an outer peripheral layer (or layers) called tunica and inner mass of cells called corpus.

Turgid - (1) Used for describing a cell which is distended being will-supplied with water.
(2) Used for describing a young of soft plant member which is stiff or rigid due to the internal pressure arising from a plentiful supply of water.

Turgor - Refers the state of a cell when the cell-wall is stretched by an increase in the volume of the vacuole by the intake of water.

Turgor Pressure - The hydrostatic pressure which is set up within a cell by the water present acting against the elasticity of the wall.

Turion - (1) A swollen perennating bud, which contains much stored food. It is formed by a number of water plants. It comes away from the parent, remains inert through the winter and gives rise to a new plant in the following spring.
(2) A scaly sucker or shoot which is arising from underground.

Tylose, Tylosis - Said of a balloon-like enlargement of the membrance of a pit in the wall of a vessel or tracheid, and a xylem parenchyma cell lying next to it. It protrudes and tends to block the cavity of the wood element.

Type Specimen - Refers to the original speciment (s) on which a discription of a new species etc., is made.

UDP - Uridine diphosphate.