"Plants have the ability to sense gravity. There are specialized parts of some cells called statoliths, which occur, for instance, in plant root cells, which need to know which direction to travel—in this case, down into the ground. The cell senses gravity, and changes its behavior accordingly.
Pollen tubes don’t have statoliths and they don’t sense gravity. A pollen tube is on a mission to find and germinate an egg; if it were primarily concerned with responding gravity, that mission would be thwarted. The pollen tube grows in the direction of the egg, and it takes its cues from the egg’s chemical signals. This means that any impact of gravity on a pollen tube is due to the actual effects of gravitational force on weight-bearing loads in nature."
Discover Magazine
