Sterile Flower - Refers to a staminate flower.

Steroids - Refer to the saturated hydrocarbons having 17 carbon atoms in a system of rings 3 six-membered and 1 five-membered, condensed together (six atoms being shared .between rings).

Sterols - There are compounds having the general chemical ringstructure of a steroid, but with a long side-chain and an alcohol group. Those found in plants (phytosterols) are oxidation products of cholesterol (C27H45OH).

Stichonematic - A flagellum having mastigonemes on one side of main axis of flagellum. Compare pantonematic, acronematic.

Stigma - Tip of carpel receiving pollens during pollination. It is having different shapes in dif rent plants and is adapted to trap pollens. In certain plants, they exhibit haptotropic movements. Stigmas are also involved in complex pollenstigma compatibility reactions.

Stilt Root - An adventitious root that is formed by a stem from a point above ground level passing downwards into the soil and imparting support to the plant.

Stimulus - Refers to any change in the environment of an organism or of part of it which is intense enough for producing a change in the activities of the living material, without itself providing energy for the new activities.

Stipe - A stalk especially the part of the thallus of certain brown algae e.g., Laminaria joining the lamina to the holdfast.

Stipules - Refer to basal appendages of a leaf or petiole. They may photosynthesize, or be scales, and may protect the axillary buds.

Stirps - A well-established variety that keeps its characters in cultivation.

Stock - (1) An artificial mating group.
(2) A rooted stem into which a scion is inserted during. grafting. I
(3) A perennial portion of a herbaceous perennial
(4) A race.

Stolon - (1) A horizontally growing stem bearing adventitious roots at the nodes, and scale leaves. New plants or tubers may develop terminally.
(2 A long hypha that is lying on the substratum and producing tufts of rhizoids and sporangiophores at intervals.

Stoma - (1) A pore in the epidermis of plants which is present in large numbers, particularly on leaves through which gaseous exchange occurs. Each stoma has been surrounded by the sausage-shaped guard cells which open and close the stoma by changes in their turgidity.
(2) It may be used to include the pore and guard cells.

Stone. Refers to the hard endocarp of a drupe.

Stone-Cell - A thick-walled cell, not much longer than broad, having lignified walls.

Stone Fruit. A drupe.

Stool - A plant from which off-sets may be taken, or with several stems arising together.

Storied - The axial cell and rays of wood that are arranged in horizontal layers as viewed in tangential section.

Strain - (l) A natural or artificial mating group that is uniform in some particular property.
(2) A variety of species, having distinct morpholiogical and/ or physiological characters.

Stratification - (1) Refers to the arrangement of some factor in horizontal layers e.g., temperature and light intensity in an aqueous ecosystem or layers in vegetation due to plants of different heights.
(2) Refers to the practice of placing seeds between layers of moist sand or peal and exposing them to low temperatures just by leaving them outside during the winter. This treatment is necessary for seeds that are requiring chilling period before germination.

Strobilus (cone). (l) Refers to the structure having distinct closely packed sporophylls (bearing sporangia) that are arranged around a central axis and produced usually at the apex of a branch as found in gymnosperms and in certain lower plants.
(2) Refers to any of the cone-like structures in angiosperms e.g., aggregate fruits of Alnus and Humulus.

Stroma. (1) A tissue-like mass of fungal hyphae in, or from which fruit-bodies are produced.
(2) The zone between the intergranum lamellae of a chloroplast.

Stroma Starch - Starch produced in the stroma of a chloroplast when photosynthesis is active.

Stromatolites - Refers to the structures which are formed and preserved in many rocks, especially carboniferous rocks that were formed by activities of algae and among the oldest organic structures recognized. They occur in gunflint chert of Ontario (about 2,000 million years old) and Precambrian rocks of Australia and Africa (about 3,000 million years old) and often consist of white concentric rings having outer ones upto a metre across.

Structural Gene - A length of DNA coding for an enzyme or other protein, equivalent to a cistron. See also regulator gene, operator gene, operon.

Style - The narrow part of the gynoecium which bears the stigma.

Sub-Climax. A community having not attained the full development possible under the prevailing conditions due to some limitations imposed by an edaphic or biotic factor.

Sub-Culture - A culture of bacteria or fungi which is prepared from a pre-existing culture.

Suberin. A complex mixture of oxidation and condensation products of fatty acids which are present in the walls of cork-cells, thereby rendering them impervious to water.

Suberin Lamelia - A layer of wall material which is impregnated with suberin.

Subicle, Subiculum - A felted or cottony mass of hyphae which may be underlying the fruit-body of some fungi.

Sub-Littoral - Growing near the sea, but not on the shore. Growing below the low water level.

Subsere - Refers to the stages in the development of climax vegetation during secondary succession in an area.

Subsidiary Cell (accessory cell). Refers to one of the group of morphologically differentiated epidermal cells that are immediately sorrounding the guard cells. Stomatal complexes lacking, subsidiary cells are known as anomocytic. Number, arrangement and method of development of subsidiary cells are having taxonomic value.