Cacti have brilliant ability to save the water in very hot and dry places where rainfall occurs rarely. This water saving ability is due to their adaptions in many structures. The cactus has either thick leaves or no leaves at all. As a result, the surface-area to volume ratio of the cactus is reduced. Surface-area to volume ratio determines how much water will evaporate. Also, the stem of the cactus is cylindrical or spherical, which also reduce the surface-area to volume.