You might have observed the tendrils of plants growing towards a support. Can you imagine how is it happening? Would you think it is responding to a stimulus?
Both plants and animals react to various stimuli around them. But the method of responding to stimuli is not similar in plants and animals. Higher animals respond to stimuli because they have a nervous system and an endocrine system. Plants do not have a well-defined nervous or endocrine system. They do have some mechanism of control by means of some chemicals or hormones.
Plants can sense the presence of stimuli like light, heat, water, touch, pressure, chemicals, gravity etc. The hormones present in the plants called phytohormones (phyto means plant) control responses towards the stimuli mentioned above. Phytohormones coordinate the activities of the plant usually by controlling one or the other aspect of the growth of the plant. So plant hormones are also called growth substances. Some major plant hormones and their action are given in the following table

Table-3: Major plant hormones and their action

Discuss with your teacher about seed dormancy

Take a glass jar and fill with soil. Sow a bean seed near the wall of the jar. This helps you to observe how root and shoot are growing. After 4 - 5 days you will notice seed germination. Keep the jar under the sun. Observe how root and shoot grows. Then tilt the glass jar and keep the plant horizontally. Observe the direction of root and shoot growth for more than a week
Does the he shoot take a horizontal tilt after a week