There is a cactus that grows only in southern Arizona and northern Mexico that has a skin around its trunk that permits it to blow up to twice its normal size.
It is the saguaro cactus, a giant desert plant. This cactus can soak up 200 gallons of water when it rains, enough to keep it from drying up during long periods without rain. But 200 gallons of water is a lot of water. How can it hold that much? Nature has constructed it so that as it absorbs water it swells, the way a balloon does when it is filling with air. After a long drink , a saguaro can double its width.
A saguaro produces 40 million seeds during its 200-year lifetime, yet not one of these may survive. Many of the seeds are eaten by animals. What’s more, these seeds cannot survive without the help of a paloverde bush or a mesquite tree.
The young seedlings need the heat of the desert to live but cannot stand the cold of the desert nights. They need the bright light of the desert but will die unless they have shade. They need summer rain but will rot if they get too much water.
The mesquite and the paloverde protect the saguaro seeds from too much water and the cold wind and provide the shade the young plants can’t live without.
