 cone

/kohn/, n., v., coned, coning.n.1. Geom.a. a solid whose surface is generated by a line passing through a fixed point and a fixed plane curve not containing the point, consisting of two equal sections joined at a vertex.b. a plane surface resembling the cross section of a solid cone.2. anything shaped like a cone: sawdust piled up in a great cone; the cone of a volcano.3. See icecream cone.4. Bot.a. the more or less conical multiple fruit of the pine, fir, etc., consisting of overlapping or valvate scales bearing naked ovules or seeds; a strobile.b. a similar fruit, as in cycads or club mosses.5. Anat. one of the coneshaped cells in the retina of the eye, sensitive to color and intensity of light. Cf. rod (def. 17).6. one of a series of coneshaped markers placed along a road, as around an area of highway construction, esp. to exclude or divert motor vehicles.7. (in a taper thread screw or bevel gear) an imaginary cone or frustum of a cone concentric to the axis and defining the pitch surface or one of the extremities of the threads or teeth.8. Ceram. See pyrometric cone.v.t.9. to shape like a cone or a segment of a cone.[148090; < L conus < Gk kônos pinecone, coneshaped figure; akin to HONE^{1}]
* * *
or strobilusIn botany, a mass of scales or bracts, usually ovate, containing the reproductive organs of certain nonflowering plants.A distinguishing feature of pines and other conifers, the cone is roughly analogous to the flower of other plants. Cones (strobili) are also found on club mosses and horsetails.* * *
in mathematics, the surface traced by a moving straight line (the generatrix) that always passes through a fixed point (the vertex). The path, to be definite, is directed by some closed plane curve (the directrix), along which the line always glides. In a right circular cone, the directrix is a circle, and the cone is a surface of revolution. The axis of this cone is a line through the vertex and the centre of the circle, the line being perpendicular to the plane of the circle. In an oblique circular cone, the angle that the axis makes with the circle is other than 90°. The directrix of a cone need not be a circle; and if the cone is right, planes parallel to the plane of the directrix produce intersections with the cone that take the shape, but not the size, of the directrix. For such a plane, if the directrix is an ellipse, the intersection is an ellipse.The generatrix of a cone is assumed to be infinite in length, extending in both directions from the vertex. The cone so generated, therefore, has two parts, called nappes or sheets, that extend infinitely. A finite cone has a finite, but not necessarily fixed, base, the surface enclosed by the directrix, and a finite, but not necessarily fixed, length of generatrix, called an element. See also conic section.▪ plant anatomyalso called strobilusin botany, mass of scales or bracts, usually ovate in shape, containing the reproductive organs of certain nonflowering plants. The cone, a distinguishing feature of pines and other conifers, is also found on some club mosses and on horsetails.▪ retinal celllightsensitive cell (photoreceptor) with a conical projection in the retina of the vertebrate eye, associated with colour (colour vision) vision and perception of fine detail. Shorter and far fewer than the eye's rods (rod) (the other type of retinal lightsensitive cell), cones are less sensitive to low illumination levels and are mediators of photopic rather than scotopic (Greek skotos, “dark”) vision. Cones are mostly concentrated within the central retina (macula), which contains the fovea (depression in the retina), where no rods are present. In contrast, the outer edges of the retina contain few cones and many rods. Chemical changes that occur when light strikes the cones are ultimately relayed as impulses to opticnerve fibres that enter the brain. See also colour vision.* * *
Universalium. 2010.