Gymnospermous. Etym., γυμνος, gymnos, naked, and σπερμα, sperma, a seed. (See Gymnogens.)
Gymnogens. A class of flowering plants, in which the ovules are not inclosed in an ovary. They are also called gymnosperms, the seeds in like manner not being inclosed in a pericarp. It includes all Coniferæ, as pine, fir, juniper, cypress, yew, cedar, &c., and Cycadeæ. All are Dicotyledonous (a few have many cotyledons), and all Exogenous, except Cycas, the growth of which is anomalous. The term is applied in contradistinction to Angiosperms, which see. Etym., γυμνος, naked, and γενεσις, increase.
Gypsum. A mineral composed of lime and sulphuric acid, hence called also sulphate of lime. Plaster and stucco are obtained by exposing gypsum to a strong heat. It is found so abundantly near Paris, that plaster of Paris is a common term in this country for the white powder of which casts are made. The term is used by Pliny for a stone used for the same purposes by the ancients. The derivation is unknown.
Gypseous, of or belonging to gypsum.
Gyrogonites. Bodies found in freshwater deposits, originally supposed to be microscopic shells, but subsequently discovered to be seed-vessels of freshwater plants of the genus Chara. See above p. [742]. Etym., γυρος, gyros, curved, and γονος, gonos, seed, on account of their external structure.
Hemiptera. An order of insects, so called from a peculiarity in their wings, the superior being coriaceous at the base and membranous at the apex, ἡμισυ, hemisu, half, and πτερον, pteron, wing.
Hornblende. A simple mineral of a dark green or black color, which enters largely into the composition of several varieties of the Trap-Rocks.
Hornstone. A siliceous mineral substance, sometimes approaching nearly to flint, or common quartz. It has a conchoidal fracture, and is infusible, which distinguishes it from compact felspar.
Humerus. The bone of the upper arm.
Hydrophytes. Plants which grow in water. Etym., ὑδωρ, hydor, water, and φυτον, phyton, plant.