If you place a seedling on its side, it will adjust its growth in response to gravity so that the shoot grows upward and the root grows downward. This is gravitropism. This behavior will occur in total darkness. Plants apparently tell up from down by the settling of structures called statoliths , which are dense cellular components such as starch grains. But the mechanism by which this movement of statoliths causes the transport and asymmetrical distribution of growth hormones within the plant is a mystery.
Hormones are in solution and are therefore themselves unresponsive to gravity.
Differential cellular growth in response to touch explains the coiling behavior of the tendrils of vines. General mechanical stimulation, such as motion in response to wind, stunts growth. A tree on a windy mountain will have a shorter, thicker trunk. This enables the plant to better maintain its attachment to the soil in windy conditions. These responses to touch and motion are examples of thigmotropism.