Most cactus species, however, changed in appearance over the years. The branches became shorter, and the leaves developed into spines. The woody stem became softer and more able to absorb and store water. Parts of the cactus. The structure of a cactus helps the plant survive in dry climates.
Most cactuses have thick, fleshy stems with waxy skin.
The stem holds water, and the skin keeps the water from evaporating. In addition, the surfaces of many cactuses can expand and contract like an accordion to accommodate the changes of water content in the stem. Cactuses have extremely long roots. The roots grow close to the surface to collect as much water as possible for storage. After a heavy rain, they can absorb a large amount of water for the plant.