I saw my son playing with a plant which was folding its leaves on mere touch. It appeared as though this plant was feeling shy of human touch. The small creeper made me curious to know about it. This sensitive shy plant is scientifically known as Mimosa pudica.This humble plant is known with variety of names like Chhui-Mui, Lajwanti, Lajjawati, Lajalu, Lajak, Makahiya, Memege etc in various parts of the world.
One of the very strange characteristic of this plant is that its leaves close even with a mild stimulus like touch. It is a favorite plant for children as they like to blow, shake, touch this plant and notice the changes within the leaves. These types of movements, shown by this plant are known as seismonastic or thigmonastic movements and are commonly seen with the plants belonging to Mimosoideae subfamily of the legume family, Fabaceae. Apart from this the leaves bend and fold in the absence of light. These movements are termed as nyctonastic movements.
Morphologically it has bipinnately compound leaf and petioles are prickly. The base of the plant leaf is swollen and is known as Pulvinus. The flexibility of the base of the leaf is due to the core vascular tissue surrounded by thin-walled parenchyma cells.
A rigid cell wall of a typical plant cell is maintained by the cell vacuoles. Water and cell contents within these vacuoles exert turgor pressure on the cell walls. Upon slight disturbance of these leaflets, chemicals containing potassium ions are released by certain regions of the stem. These chemicals force water out of the vacuoles of the cells present in leaves. As a result water is diffused out of the cells decreasing the turgor pressure. The turgidity levels vary between different regions of the cell. This makes the small leaflets close and the pulvinus bend leading to the collapse of leaf petiole. The stimulus gets transmitted to the neighboring leaves slowly.
Why should a plant behave in such a way? Living beings try to defend themselves from predators. For example we have receptors in our skin which responds to touch. Plants are consumed by herbivorous animals which are scared of fast-moving plants. A touch-me-not plant shrinks on mere touch hence animals avoid this plant and consume a less active one. This plant prevents harmful insects like grasshopper or locust from sitting on it in two ways. The first method is folding of its small leaflets suddenly upwards. Due to this the leaflets appear like small twigs which are unappetizing for the insects. If this mechanism fails to flee away insects, the leaves start drooping down. This exposes the thorny petioles to the insects and the plant gets rid of them.
The fact the plants also feel pain and understand affection was proved by an Indian scientist, Jagadish Chandra Bose. This plant was declared as the plant of the week during October 12-22, 2001.