_Conductivity._ Power to conduct (heat or electricity). _Conductor._ That which readily conducts (heat or electricity). _Congeal._ Solidify, freeze. _Connate._ United from the beginning. _Constant._ A quantity that does not vary, or one that does not change under given conditions. _Convex._ Curved like the outside of a circle or sphere. _Coördinate._ Each of a system of magnitudes used to fix the position of a point, line, or plane. _Copernican._ Relating to the theory that the planets (one of which is the earth) move around the sun. _Copper._ An important metallic element. Symbol: Cu. _Corolla._ The inner envelope of a flower. _Corona._ A small disk of light around the sun or moon. An appendage on top of a seed or the inner part of the corolla. _Cotyledon._ One of the first leaves in the embryo of a higher flower. _Coulomb._ The amount of electricity carried in one second by one ampere. _Cretaceous._ Of or like chalk. Relating to the last Mesozoic period. _Cri._ The common respiratory infections, such as the common cold, influenza, etc. _Criminology._ The scientific study of crime and criminals. _Cross-pollination._ The transfer of pollen from the anthers of one flower to the stigma of another flower of the same kind. _Crustacea._ A class of hard-shelled arthropods, including lobsters and crabs. _Crystal._ An aggregation of molecules with definite internal structure and external form of a solid enclosed by symmetrically arranged plane faces. A crystal is formed when certain liquids or gases solidify (crystallize). The study of crystal structure is crystallography. _Ctenophora._ A class of low animals comprising certain jellyfish. _Cycle._ A series of operations in a heat engine. A two-cycle engine is one with a cycle of two strokes. Properly, it should be called a two-stroke-cycle engine. _Cyclone._ A violent wind of low diameter. A circular wind system about an area of low pressure. _Cyst._ A hollow organ containing a liquid secretion. _Cyto-._ Cell-, in compounds. _Cytoplasm._ Cell protoplasm, not including the nucleus. _Darwinism._ Organic evolution in general. The theory that the origin of species is due to natural selection, as developed by Charles Robert Darwin. All biologists worthy of the name believe in evolution, but by no means all accept Darwinism in the narrow sense. _Declination._ The angular distance of a heavenly body north or south of the celestial equator. The deviation of a magnetic needle from true north. _Decurrent._ Extending downward, as the base of a leaf. _Dehydrate._ Remove water, dry. _Dendrology._ The scientific study of trees. _Devonian._ Of the geological formation between the Silurian and the Carboniferous. _Dew point._ The temperature at which the air is saturated with water-vapor. _Diadelphous._ Formed into two bundles. (Of stamens.) _Diandrous._ With two stamens. _Dielectric._ Insulating, insulator of electricity.