from
The Collaborative International Dictionary of English v.0.48
Exogen \Ex"o*gen\, n. [Exo- + -gen: cf. F. exog[`e]ne.] (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.
[1913 Webster]