• (a.) Having the longer axis vertical; -- said of erect stems.
Or`tho·trop'ic adjective [ See Orthotropal .] (Botany) Having the longer axis vertical; -- said of erect stems. Encyc. Brit. 
Type: Term Pronunciation: ōr′thō-trop′ik Definitions: 1. Extending or growing in a straight, especially a vertical, direction.
orthotropic In botany, growing vertically with reference to developing plant organs that grow nearly vertically, either upward or downward.
noting, pertaining to, or exhibiting a mode of vertical growth.