*geotropism*

n. [ Gr. ge`a, gh^, the earth + &unr_; to turn. ] (Biol.) A disposition to turn or incline towards the earth; the influence of gravity in determining the direction of growth of an organ. [ 1913 Webster ]

☞ In plants, organs which grow towards the center of the earth are said to be positively geotropic, and those growing in the opposite direction negatively geotropic. In animals, geotropism is supposed by some to have an influence either direct or indirect on the plane of division of the ovum. [ 1913 Webster ]