The Collaborative International Dictionary of English v.0.48:

Endogen \En"do*gen\, n. [Endo- + -gen: cf. F. endog[`e]ne.]
   (Bot.)
   A plant which increases in size by internal growth and
   elongation at the summit, having the wood in the form of
   bundles or threads, irregularly distributed throughout the
   whole diameter, not forming annual layers, and with no
   distinct pith. The leaves of the endogens have, usually,
   parallel veins, their flowers are mostly in three, or some
   multiple of three, parts, and their embryos have but a single
   cotyledon, with the first leaves alternate. The endogens
   constitute one of the great primary classes of plants, and
   included all palms, true lilies, grasses, rushes, orchids,
   the banana, pineapple, etc. See Exogen.
   [1913 Webster]

WordNet (r) 3.0 (2006):

endogen
    n 1: a monocotyledonous flowering plant; the stem grows by
         deposits on its inside [syn: monocot, monocotyledon,
         liliopsid, endogen]