Explain different types of tactic movement.

Tactic movements are the movements in response to stimulus. Some tactic movements in plants are:
 

Phototropism

The growth movement in plants in response to light stimulus is known as phototropism. For example, the flower head of a sunflower is positively phototropic as it moves from East to West, along with the movement of the Sun.

In the above activity, the shoots show positive phototropism, while the roots show negative phototropism.

Geotropism

The growth movement in plants in response to the force of gravity is known as geotropism. In geotropism, the roots of the plant always grow downwards, while the shoots always grow upwards, away from the earth.

Chemotropism

The growth movement in plants in response to chemical stimuli is known as chemotropism. For example, the growth of pollen tube towards the ovule in the ovary (through the stigma and style) is an example of positive chemotropism.

Hydrotropism

The growth movement in plants in response to water is known as hydrotropism. For example, the roots of some plants grow towards the water source, even when the water source is not present directly below it.