"growth downward," 1874, from geo- "earth" + -trope "a turn, direction" (from PIE root *trep- "to turn"), translating German Geotropismus (1868), which was coined in 1868 by German botanist Albert Bernhard Frank. Related: Geotropic.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit trapate "is ashamed, confused," properly "turns away in shame;" Greek trepein "to turn," tropos "a turn, direction, course," trope "a turning;" Latin trepit "he turns."
1899, "tendency of an animal or plant to turn or move in response to a stimulus," 1899, abstracted from geotropism or heliotropism, with the second element taken in an absolute sense; ultimately from Greek tropos "a turning" (from PIE root *trep- "to turn").
<a href="https://www.etymonline.com/word/geotropism">Etymology of geotropism by etymonline</a>
Harper, D. (n.d.). Etymology of geotropism. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/geotropism