That is interesting, because very likely our readers might in crossing a desert be perishing of thirst when a Bedouin Arab would be perfectly happy. The plants have learnt to do without water just in the same way as the Arab has done.
Of the many interesting desert plants, the Succulents, Cacti, Euphorbias, and others of the same extraordinary, fleshy, dropsical appearance, come first.
When a Cereus plant (one of the American Giant Cacti) was dried, it did not lose the whole of its water for 576 days. That is probably the longest time "between drinks" on record. A Houseleek (Sempervivum), which has to grow on dry rocks where it has no water for days together, remained quite fresh for 165 days.
Giant Cactus near Aconcagua Valley, Chile
This plant was about 8 feet high. The darker part on the tallest branch is the dark red flower of the parasitic horanthus. The thorns covering the branches are quite distinct.
There are several reasons why these plants took so long to dry up. To begin with, they have inside their stems and leaves certain substances which hold water and delay its escape. Moreover their extraordinary shapes are of very great assistance. They prefer globular, round, circular, pear-shaped, or cylindrical forms.
Suppose you were to cut such a round mass into thin slices and lay them out flat, it is quite clear that they would cover a much greater surface. Thin leaves also, if squashed up into a round ball, would have a very much smaller surface.
The water can only escape from the surface exposed, so that these condensed round balls and fleshy columns have far less water-losing surface than ordinary leaves.