geotropism
noun
ge·ot·ro·pism jē-ˈä-trə-ˌpi-zəm 
: a tropism (as of plant roots or shoots) in which gravity is the orienting factor : gravitropism
Exactly how roots perceive and transduce gravity has not yet been fully explained, which is surprising because root geotropism has been investigated for more than 100 years.
Lewis J. Feldman
Lewis J. Feldman
Word History
Etymology
borrowed from German Geotropismus, from geo- geo- + -tropismus -tropism
Note: The term was introduced by the German botanist and plant physiologist Albert Bernhard Frank (1839-1900) in Beiträge zur Pflanzenphysiologie (Leipzig, 1868), p. 85.
First Known Use
1873, in the meaning defined above
Medical Definition
geotropism
noun
ge·ot·ro·pism jē-ˈä-trə-ˌpiz-əm
: a tropism in which gravity is the orienting factor