The tendency of plant roots and shoots to grow in response to gravity, with roots growing downward and shoots growing upward.
From Greek 'geo-' (earth) and 'tropos' (turn, direction). The term emerged in the 19th century as botanists studied how plants orient themselves relative to Earth's gravitational field.
Plants don't have eyes or brains, yet they somehow 'know' which way is down—this is because specialized cells in root tips contain starch granules that settle with gravity, sending chemical signals to redirect growth. It's like nature's built-in compass.
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