Thorns are the modified aerial stem structures. These are stiff, pointed, straight, hard and sharp structures that have lost their point of growth. Thorns are basically formed to protect the plants from grazing and excessive transpiration. These structures have the vascular system surrounded by a bark of thick-walled cells.
In Bougainvillea, the axillary bud gets modified into a woody thorn. Thorns are curved in Bougainvillea which helps the plant in climbing.
