Welcome to You Ask Andy

Pamela June Payne, age 11, of Fayette, W.Va., for her question:

HOW CAN CACTUS LIVE WITHOUT WATER?

When we think of the desert, we immediately conjure up visions of flat, desolate expanses of land, dry and hot. Our vision may contain a dry barren lake or shimmering hot sand dune. Occasionally a cactus plant will appear, proud and alone, almost daring in its staunch determination to survive in such a harsh, waterless environment.

Because it is such a thrifty hoarder, the cactus plant lives with a minimum of water. Many varieties have vast spreading root systems covering large areas close to the ground's surface. When a brief rain occurs, these roots absorb the welcome water almost instantly.

The stems of cactus plants are usually plump and  swollen, sometimes forming

huge water stores. Often they are

pleated, which allows them to stretch out, providing more room

still for water storage. Some, such as the barrel cactus, are like enormous water butts, while others, like the saguaro cactus, form long tube like columns stretching high into the sky.

A cactus plant doesn't really have leaves through which water can be lost by evaporation. What's more, since cacti are so compact, their surface area is relatively small ¬another important plus in keeping water loss down. The cactus plant not only knows how to absorb water quickly in the brief instances when it is available, it also has the lowdown on how to keep it. In one laboratory experiment a cactus plant was left unwatered for several years. Guess what?  it lost only a third of its precious moisture!

The prickly cactus is a perennial plant, and some varieties can live for hundreds of years. The more than 1,300 species of cacti generally grow very slowly because of their boom or bust diets. Although the cacti family originated in America, many species are at home in other parts of the world.

We might think that the prickly thorns a cactus wearswould be enough to discourage any living creature from coming near it. Not so. At the peak of the dry season, the prairiejack rabbit gorges himself with cactus stems as a plentiful source of water. Many of the large cacti serve as hotels for small birds and rodents. The tiny cactus wren, for example, knows her nest and chicks are safe from hungry predatory snakes who won't hassle the barbs and thorns.

In years past, desert Indians well knew the value of certain cacti, particularly the saguaro. They mashed its stems for nourishing liquids, ate its tasty fruit and made butter from its seeds. Even when the plant died it was useful, for its remains could be burned as fuel..

When the brief rains arrive, the desert is transformed into a brilliant display of color. As if to say thank you, the cacti put on a show of blossoms in vivid hues of red, orange and yellow. One, the hedgehog cactus, dons a gorgeous garment of pinkish red blossoms. When these fade, a cluster of strawberry¬flavored fruit remains.

 

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