Re: [math-fun] Polynesian (Pacific Ocean) navigation pre-clocks, pre-GPS

Bees have an internal clock, and they also keep track of the sun. The combination gives them direction information adequate for their (short distance only) needs. I think some other animals track stars, but do not recall the details. (It would probably be long distance migrating birds or insects.) Some bacteria also have magnetic compasses, which they use to keep track of "up" versus "down." Question: How do plant seeds, when germinating deep, know which way is "up"?