Growing by additions on the outside; specifically, in botany, belonging to or characteristic of the class of exogens.Produced on the outside, as the spores of hyphomycetous and many other fungi; growing out from some part: specifically applied in anatomy to those processes of a vertebra which have no independent ossific centers of their own, but are mere outgrowths.In geology, applied by Von Humboldt to extrusive, volcanic rocks, in contrast to endogenous rocks. See endogenous, 3.