The descending, and commonly branching, axis of a plant,
   increasing in length by growth at its extremity only, not divided into
   joints, leafless and without buds, and having for its offices to fix
   the plant in the earth, to supply it with moisture and soluble matters,
   and sometimes to serve as a reservoir of nutriment for future growth. A
   true root, however, may never reach the ground, but may be attached to
   a wall, etc., as in the ivy, or may hang loosely in the air, as in some
   epiphytic orchids.