geotropism

/dʒiˈɑtrəˌpɪzəm/

Geotropism is when plants and fungi respond to gravity by growing in a certain direction. Typically, roots grow in the direction that gravity pulls, and stems grow in the opposite direction.

Root down, stem up seems such a basic fact to us that it's easy to assume that all plants always grow in a straight line from root to tip. If that was true, though, putting a plant on its side would mean it would go from growing completely vertical to completely horizontal. Instead, if you put a houseplant down sideways, its stem will start to grow upward, curving until it's once again growing the opposite direction of gravity's pull. That's an example of geotropism.

Definitions of geotropism

1. noun

   an orienting response to gravity
   type of:

   tropism

   an involuntary orienting response; positive or negative reaction to a stimulus source