Supperssive - Used for a plasma gene which suppresses the expression of an alternative condition in a particular respect in a hybrid individual and its descendants.

Suppressor - A gene, one of whose allelomorphs renders indetectable the difference determined by the allelomorphs of another gene.

Surface Area/Volume Ratio - Refers to the ratio of the surface area of a cell, organ or organism to its internal volume. This ratio directly relates to the possibility of gaseous exchange and absorption of dissolved mineral. Hence size of unicellular organisms is limited by the rate of gaseous exchange from surroundings whereas in higher plants leaves and intercellular space results in a much higher ratio.

Susceptibility - The whole properties of a plant, which dispose it to be attacked by a parasite.

Suspension Culture - Refers to the system of single cells and small cell aggregates in a liquid growth medium which is kept agitated by bubbling, shaking or stirring to prevent settling of cells.

Suspensor - (1) A cell that is supporting the gametangium of the Mucorales.
(2) A structure that is developed with the embryo of seed plants and some pteridophytes, elongating and pushing the embryo into the nutritive endosperm or prothallus.

Swamp Refers to-a region of stagnant or slow-flowering water having vegetation of reeds, sedges and yellow flagiiris etc It is formed around lake margins, on water retentive clays in desert and semidesert areas. Mangroove swamps are formed along tropical coasts having vegetation of halophytes.

Swarm-Cell - Of myxomycetes, and some Chytridiales, a motile cell acting, before and after division, as an isogamete.

Switch Plant. A plant having small leaves, often reduced to nonfunctional scales, and long thin stems and branches, with photosynthetic tissue in their cortical regions.

Syconium, Syconus. The fruit of a fig, which consists mainly of the much - enlarged receptacle of the inflorescence.
Symbiosis - Used for describing a type of mutualism that is taking place between two organisms of different types in which both the interacting organisms mutually benefit each other and generally live in harmony with each other e.g., relationship existing between algae and fungus in a lichen thallus or between Rhizobium bacterium and leguminous plant.

Sympatric. Used for describing two or more populations that can interbreed but usually do not do so because of various difference e.g., different flowering times, different pollinators etc. Such population may become so distinct so as to form separate species due to natural selection.

Symplast - Refers to the continum of cell protoplast throughout the plant linked by plasmodesmata. As it is offering far greater resistance to water flow than the apoplast, it is only a secondary route for water movement.

Symplastic Growth - Refers to a type of growth in which adjacent cells grow at the same rate so that the symplast does not get disrupted.

Sympodial Branching - Refers to a type of growth in some plants e.g., elm and lime, in which apical bud is withering at the end of growing season and lateral buds immediately below it continue the growth in the next season.

Sympodium - A composite axis which is produced and increased in length by successive development of lateral buds, just behind the apex. The main axis stops growing.

Synandrium - A mass of united anthers.

Synadrous - Having several united stamens.

Synangium - A compound structure which is formed by the lateral fusion of sporangia. It is found in certain ferns.

Synapsis - Refers to the pairing of homologues during prophase I of meiosis. Pairing is very exact process which starts from centromeres and continue with pairing of chromosomes at various point along the length of homologues. Contraction of chromosomes continues during the pairing and chromosomes become closely coiled around each other to form bivalents. Nature of forces causing pairing of homologues is not clearly understood.

Syncarpous. Refers to a gynoecium in which two or more carpels get fused and the degree of fusion varies in different species, The gynoecium, that is joined only at the base of ovary (e.g., in Labiatae) is known as semicarpous, that is joined from ovary to style is known as synstylovarious(found in Caryophyllacea) and that is joined from ovary to stigma is known as syncarpaus (e.g., in Cruciferae).

Syndesis. In meiotic nuclear division, the fusion of homologous chromosomes.

Syndetocheilic. Refers to gymnosperm stomatal complex in which subsidiary cells and guard cells are derived from the same initial cell e.g., in Bennettitales.

Syndiploidy - Doubling; the fusion of sister nuclei to yield a doubled chromosome number, particularly in the divisions immediately precedings meiosis.

Syndrome - A group of symtoms which are characteristic of the same infection or abnormal genetic condition, but not necessarily all appearing together.

Synecology - Refers to the study of plant communities.

Synergidae, Synergids - The two cells, which, together with the egg nucleus form the egg apparatus of the embryo sacof flowering plants.

Synergism - (1) The combined activities of agencies such as drugs, hormones etc., which separately influence a reaction in the same direction, such that the effect produced is greated than the sum of effects of each agent alone.
(2) A similar effect which is brought about by two organisms.

Syngamy. The fusion of gametes.

Syngenesious - Refers to an androecium in which anthers get fused but filaments are free as in Compositae.

Syntype - Any one of two or more specimens of other material (descriptions, illustrations etc.) designed by an author in the original publication of the name of a taxon. As a taxon can have only one type, a lectotype is subsequently chosen from a group of syntypes for serving as the nomenclatural type.

Systematics. Refers to the study of the classification of living things, laying emphasis on their evolutionary relationships.

Systemic (translocated). Refers to a chemical which is absorbed by a plant and translocated throughout the tissues e.g., systemic fungicides and insecticides.