PH
Plants don't rely entirely on sunlight to determine their orientation.
Specialized cells contain dense starch-filled structures called statoliths that settle under gravity.
This helps roots grow generally downward and shoots orient upward, a response known as gravitropism.
Experiments in space have helped scientists investigate what happens when normal gravity cues are dramatically altered.
A germinating seed buried in darkness still has a biological way of determining which direction it should grow.
© NASA