These two tropisms occur in any kind of condition - In this experiment, we will test to see how plants react to light. Put soil mix into both the containers at equal levels and put 3-4 seeds in each container. Allow the plants to grow about an inch tall with sufficient water and light. Place the container on its side and put it in a room with light coming only from the left-hand side. Leave the jar still for about 2-3 days.
Observations made are that the plant changes direction and grows towards the light .
Growth in plants takes place with the help of substances called auxins . In normal conditions, with sufficient light, the plant grows straight up since the auxins are evenly distributed. But in the experiment when the stem starts to grow upwards, the light does not fall evenly on all sides of the plant . Auxins get collected on this dark side which causes the darker side to grow and elongate. As the other side has a deficiency of auxins, it does not grow.