Torus - (1) The receptacle of a flower.
(2) The thicker part of the cover of a bordered pit.

Totipotency. The capacity shown by certain types of isolated differentiated plant cells for regenerating the whole plant.

Touchwood - Used for wood which is much decayed by fungal attack. It crumbles teadily, and gets easily ignited by a spark when dry.

Toxin - Any poisonous substance which is of mocrobial origin. It stimulates the formation of antitoxins in the animal body. Many bacterial diseases are caused by exotoxins and endotoxins. There are serveral fungi which produce toxins. Toxins produced by Asper-gillus nigerare known as afflotoxins. In higher plants toxins are not much common e.g., ricin in castor oil brings about agglutination or red blood corpuscles..

Trabacula - A bar-like structure which is extending across a lumen or lacuna. For example, there are certain endodermal cells which elongate radially to form trabaculae in endodermis of stem of Selaginel. In some plants there are extensions of secondary wall thickening which are forming trabaculae across lumina of xylem tracheids.

Trace Element An element which is required in very small amounts by a plant for healthy growth and development. Generally it is a metal which is involved in the structure of an enzyme complex.

Tracer - An isotope which is incorporated in into a compound of biological importance, so that it become possible to follow the passage of the isotope atoms through the physiological processes of the plant.

Tracheid (E). A long narrow pipe-like, non-living cell with norrowed shut ends and thick walls, in touch with other vessels through the pits, present in wood, specially that of ever green trees, for giving support and transporting water.

Tracheary Element A water - conducting cell xylem i.e., a vessel element or trachied. The secondary cell walls of the tracheary elements show various types of thickening (see illustration). Annular and spiral patterns of thickening allow further extension of the tracheary element and tend to be found in protoxylem. The other forms of thickening are seen in metaxylem. Although bryophytes do not possess xylem, some do possess water-conducting cells known as hydroids. Some consider these are also tracheary elements.

Trama - In an agaric, the somewhat loose network of hypae forming the middle part of a gill.

Transmission - Refers to the transfer of virus of a disease from infected plant to a healthy plant.

Transamination - Refers to the transfer of amino group to a keto group catalysed by transminases. It is important in amino acid metabolism.

Transcription - Refers to the process in protein synthesis in which complementary copy of nuclear genetic code is formed by synthesis of mRNA molecole.

Transaminase - An enzyme carrying out transamination.

Transduction - The transfer of genetic material from an invaded and lysed bacterium to another bacterium by a bacteria phage.

Transect - A lint or belt of vegetation which is selected for charting plants. It is done to observe changes in the composition of the vegetation across a particular area.

Transferase - Refers to any enzyme catalysing reactions in which a functional group is transferred from a donor to an acceptor molecule. Six classes of such enzymes are known including phosphotransferase or kinase, phosphate acyltransferase etc.

Transfer RAN (tRNA). Refers to a type of RNA molecule that is shaped like a clove leaf. It binds to amino acid in cytoplasm, them transfers the Bound amino acid to the site of protein synthesis and finally leaves the attached amino acid at correct position by recognizing the site which is dictated by RNA codon and recognized by tRNA anticodon. This it is important in translation of genetic code into protein polypeoptide.

Transformation - Refers to the introduction of genetic material from dead bacteria in suspension to living bacteria in same suspension.

Transfusion Tissue - A tissue that is lying on either side of the vascular bundle in the leaves of most gymnosperms. It represents an extension of the vascular bundle carrying out the function of lateral veins. It is composed of empty cells with pitted and occasionally internally thickened walls, and parenchymatous cells which have protein.

Transition - Refers to a mutation which is caused by substitution in the DNA of one purine base for another or one pyridine for another. Adenine and guanine could replace each other as can cytosine and thymine.

Transition Cell - A thin-walled cell at the end of a leaf which is representing the last of the phloem. .

Transition Region - The portion of the axis of a young plant in which thchange from root structure to stem structure takes place.

Transitional - Used for an inflorescence which has some recemose and some cymose characters.

Translation - Refers to the part of the process of protein synthesis in which there occurs decoding of the message of codons in mRNA and concurrent formation of polypeptide chain based on the sequence of triplet codons. It takes place on ribosomes in cytoplasm of cell and also involves tRNA. The process is highly endergonic and needs a 4ATP equivalents per amino acid residue. Four stages are recognised in the process: activation initiation, elongation and termination.

Translocation - (1) Refers to the movement of soluble organic food material etc., through tissue.
(2) Refers to the transfer of part of a chromosome into a different part of a homologous or into a non homologous chromosome.

Transmitting Tissue (conducting tissue). Refers to the specialized, thin walled tissue that forms the central portion of the style in some angiosperms through which pollen tube grows down to the funiculus. It may take part in self-incompatibility system.

Transpiration - Refers to the loss of water by evaporation from the plant surface, over 90% of which takes place through stomata (stomatal transpiration)and about 5% takes place directly from the surface of epidermal cells. Transpiration from the general surface of the plant body and not taking place through stomata is known as cuticular transpiration.

Transpiratton Current Transpiration Stream - Refers to the stream of water which passes through a plant from the roots to the leaves, whence it escapes, chiefly in the form of water vapour.

Transversion - Used for a mutation which is caused by substitution of a purnie base for a pyrimidine base (or vice versa) in the DNA.

Trap Crop - Refers to any crop that is planted in or around another crop to attract pests away from the valuable crop. Trap crops are generally heavily treated with pesticides, burnt or ploughed in.

Tree - A tall, woody, perennial plant that is having a well marked trunk with few or now branches persisting from the base.

Tree Ferns - Refers to some members of fern order Filicales that attain heights of 10m although secondary tissue is not clearly developed. In these species, the stem is strengthened by the bands of sclerenchyma.