. tropic movements
What are tropic movements? Briefly explain various types of tropic movements in plants.
Growth movements occurring in response to unidirectional external stimuli in a plant part are called tropic movements.
The types of tropic movements in a plant are,
Phototropism means movement towards the light. The plants grown in light illuminating them from all directions grow more or less upwards. But if the light is brighter on one side of the plant than another (unilateral light), then the shoot of the plant will bend towards the increased light and the roots, if they are exposed, will grow away from it.
The term geotropism means growing towards the earth’s gravity. It is also called gravitropism. Organs which grow towards the gravity are positively geotropic and those that grow away from the gravity negatively geotropic.
The movement of plant parts in response to water or moisture is called hydrotropism. When a plant part grows towards the source of moisture, it is said to be positively hydrotropic. The growth of roots towards moisture ensures that roots will be near the water available in the soil.
The growth movement of plants in response to a touch stimulus is called thigmotropism. Some interesting response is seen in response to touch. Plants such as sweet peas, Cuscuta and vines have tendrils which coil around other plants in response to one-sided contact or touch. The stimulus is perceived by tendril tips and then it is transmitted to basal parts.
Chemotropism is the phenomenon of the growth of plant organs in response to chemicals. The movement of pollen-tube of angiosperms and gymnosperms towards sugars and peptones secreted by neck canal cells of the female gametophyte is an example of chemotropism.