Ex"o*gen (?), n. [Exo- + - gen: cf. F. exogène.] (Bot.) A plant belonging to one of the greater part of the vegetable kingdom, and which the plants are characterized by having c wood bark, and pith, the wood forming a layer between the other two, and increasing, if at all, by the animal addition of a new layer to the outside next to the bark. The leaves are commonly netted-veined, and the number of cotyledons is two, or, very rarely, several in a whorl. Cf. Endogen. Gray.