Scanning electron micrograph of a bristles (glochids) of the cactus Opuntia aurantiaca. Bristles & the sturdier spines develop from the stem buds, which in cacti are paired; the lower bud forms the spine, the upper one the branches or flowers. The upper bud may be protected by fine bristles. The tip of the bristle is barbed while the body is spirally structured for rigidity. They slide in easily, withdraw painfully, or break off in the skin. Spines & bristles protect the plant from grazing animals, an important function in their native arid habitat. They also protect the stem from intense sunlight. Magnification: X1800 at 10x8 inch, x514 at 6x7cm size.