A cactus stem is used for storing water.
Cactuses store water, serving as their own reservoirs and surviving long droughts.
Cactus stems hold water to survive droughts.
How does a cactus survive droughts?

[1] It becomes dormant
[2] It helps them survive
[3] roots and shoots
[4] high humidity
[5] circulatory systems
[6] roots to grow
[7] Holding water in the stem
[8] dormant state