Exogen

[Gr. exo, outward, and genos, race, offspring, cla , from gignomai, anciently geno, to come into being. See GENDER.) ( Bot. ) A plant whose stem is formed by succe ive additions to the outside of the wood; one of the cla Exogens. Ex'ogens, n . pl . ( Bot . ) In the cla ification of Lindley, the 7th and largest cla of plants. It is characterized by having the leaves reticulated; the stems with a distinct deposition of bark, wood, and pith; the embryo with two cotyledons; and the flowers usually formed on a quinary type. A transverse slice of the stem (Fig. 53) exhibits a central cellular substance or pith, an external cellular and fibrous ring or bark, and an intermediate woody ma , with certain fine lines radiating from the pith to the bark through the wood, called medullary rays. They are called Ezogens because they add to their wood by succe ive external additions. The cla Exogens corresponds to the cla Dicotyledones of other botanists. See DICOTYLEDON, and, chiefly, AGE OF PLANTS. Exogenous, (els-jen-us,) a. Pertaining to the cla of plants that grow on the outside; growing by succe ive additions to the outside of the wood, as the stems of the greater number of plants. Exogo'nium, n. [Gr. ezo , without, and gonia , angle.] ( Bot . ) A genns of plants, ord. Convolvulacese . The species E. purga is a native of Mexico, near Chincanquiaco. Its tubercular roots constitute the true jalap of the Materia Medica, so well known as a purgative. Ex off i'cio. [Lat., by virtue of office or duty.] In general language, every act done by an officer either in prosecution of the general duty of his office, or in exe cution of some duty imposed by it, is said to be done ez officio. But, in more strict phraseology, a proceeding ex officio is one taken by an officer of his own will, in exe cution of what he takes to be the duty of his office; as where a justice of the peace demands and takes surety at his own discretion, without the request of the injured party.