Here are the starch statoliths that settle out of the cytoplasm to the "bottom" of the columella cells, allowing them to detect the direction of "up".I.E. Plants and trees grow towards the maximum source of sunlight (following it by maintaining an average position with respect to it’s daily movement).
If the source of light is rigid, they grow straight for it.
The plant’s ability to use (or need to use) is likely miniscule, and may only be used in a very brief period when it is underground.
A seed sprouts due to moisture and temperature (change). The temperature change is a direct result of sunlight. The sprouting seed pursues the source of that warmth to reach the surface. In that case it may be following infra-red rather than visible solar.
The use of ‘gravity’ to determine direction of growth is an unproven theory, and seems to have very little effect compared to the source of heat and light.
If you can point me to a documented source which can prove that seeds use ‘gravity’ to determine direction, I would be glad to read it.
http://www.plantphysiol.org/cgi/content/full/133/4/1677
As discussed in our previous Update (Chen et al., 1999), different cells are specialized to carry out these successive phases of gravitropism in monocots and dicots. For instance, in roots, gravity is perceived mainly by the columella cells of the root cap, whereas the differential growth response associated with gravistimulation occurs in the elongation zone (EZ; Figs. 1A and 2). In shoots, cells located in specialized tissues at the periphery of the vasculature, including the endodermis of hypocotyls (Fig. 1B), and the bundle sheath parenchyma in inflorescence stems and cereal pulvini perceive gravity and generate a signal that is transported laterally to the more peripheral tissues.
Here are the starch statoliths that settle out of the cytoplasm to the "bottom" of the columella cells, allowing them to detect the direction of "up".