Читать книгу The Circle of Knowledge: A Classified, Simplified, Visualized Book of Answers - Various - Страница 214

There are few plants so well armed as the Cactus, the evident design of which is to conserve its moisture. This is accomplished in several ways. Of course, the very shapes of the plants are all in their favor. Being either round, globular, or cylindrical, they offer a limited surface to the dry air inconceivably less than a plant of the same size bearing a quantity of leaves. The thick skins, too, play a big part in keeping in the moisture, and many kinds of cacti, such as that known as Old Man’s Beard, are covered with dense masses of hair.

Many of these succulent desert plants grow to a great size. Thus the Giant Cactus sends up a tall column, often with only a very few branches, which may be eighty or even one hundred feet in height.

Curiously enough, some cacti produce the most beautiful flowers, blossoms without rival in the whole world. The various kinds bear flowers of every conceivable shade except blue, and the blooms are often of an immense size. It is not unusual for the blossoms to measure eighteen inches, or even two feet, across.

Living as they do in arid regions, cacti are peculiarly liable to be attacked by thirsty animals. Now, a common mode of defense is the covering of the plant with sharp spines. These spines are so arranged that they completely shield the juicy stem from any possibility of attack, it is said that on occasion Mexican ponies will try to knock a cactus to pieces with their heels when they are thirsty. More often than not the animals suffer cruelly for their temerity by being severely pricked.

In much the same way the Aloes and Agaves are protected, so that a hedge of these plants when placed round a field, is better than the most perfect barbed wire fence.