To find out the effect of Gravity on growth of Roots and Shoots.
To show the effect of gravity on the direction of growth of the root, germinate bean seeds in a roll of damp cloth and select a seedling with a nearly straight root and stem. Line the inside of a gas-jar with damp blotting paper and pin the selected seedling through its cotyledons to the centre of the cork of the gas-jar. Fit the cork to the gas-jar in a horizontal position so that the seedling is horizontal in the centre of the jar and place the jar in a dark room. The set-up is thus so arranged that the plant is equally surrounded by moisture on all sides, and the light effect is absent. Another seedling should be pinned on a klinostat as a control.
Make observations every hour. The tip of the root turns downwards while the stem bends upwards. The force which has caused these changes in the direction of growth is gravity. Hence the force of gravity causes roots to grow downwards and shoots upwards.
In any position a seed is planted the main root eventually grows downwards and the main stem upwards. This means that roots are positive in their response to gravity - positive geotropism and shoots are negative - negative geotropism. It is also possible to show geotropic effects in shoots and roots much more simply. A potted seedling is placed on its side in a dark room and left overnight. The shoot grows upwards while the roots on examination will be found to have bent downwards again.