Plants can detect “up” by sensory cilia at the “bottom” of a cell getting disturbed by pellets that settle out of the cytoplasm.
Geotropism is essential for the young spout to grow UP out of the soil.
Once up out of the soil, a plant uses heliotropism to turn its leaves towards the Sun. It doesn't grow towards the sun, as much as it turns towards the sun; because where the sun is changes during the day. Heliotropism is accomplished by swelling tissues with water, while evacuating other tissue of water- causing the stem to twist, turning the leaves towards the sun; facing East in the morning and west in the evening.
I have watched over a period of months, a set of vines take off horizontally, then up a hill, then directly to an abandoned car bumper, and wrap themselves around it.
Is it because the car bumper is an extreme source of gravity?
I understand what you are saying, however I think it odd the way you say it.
“It doesn’t grow towards the sun, as much as it turns towards the sun; because where the sun is changes during the day.”
That is like saying that if I am trying to get my sailboat back to port, and I have to tack to keep on course, I’m not really heading to port.
A question. Why do you think it is important that certain seeds be planted at certain depths?
(Hint: It has nothing to do with gravity)
Sorry to be bothersome, but another question rears it’s head.
Why do roots grow downward? Is this caused by gravity as well?