The Sandbox tree is a native of tropical America. The fruit, as large as an orange, consists of a number of rounded pieces, each with a single seed inside. When ripe each piece splits off, making a noise like the report of a pistol. The plant is sometimes called the Monkey's Dinner Bell. These pieces may be thrown to a distance of fifty-seven feet from the parent plant. Even more remarkable are the hygroscopic grasses. There are four of them, which are widely separated as regards distribution, for one (_Stipa capillata_) lives in Russia, another (_Stipa spartea_) in North America, a third (_Aristida hygrometrica_) is found in Queensland (Australia), and the fourth (_Heteropogon contortus_) belongs to New Caledonia. Yet all these four grasses are said to kill sheep, and do so in a manner that is almost identical. The mechanism is as follows. The fruit is like that of most grasses, enclosed in a folded leaf, the bract (or glume), which in these particular cases is produced into a very long fine tapering hair or awn. This awn is sensitive to changes in the _moisture_ of the air. It is strongly hygrometric: in wet weather it straightens itself, and it coils into corkscrew spirals in dry weather. The widened part of the base, which contains the grain, tapers into a sharp, very hard point; upon this there are, on the outside, many stiff hairs, which point backwards away from the sharp tip. Now, suppose this fruit to fall on the ground, the awn or tail is sure to be entangled in neighbouring grasses or herbs, but the hard point will rest upon the ground. Every coil and twist made by the entangled awn or tail will push the point a little deeper into the earth, and the backward-pointing stiff hairs will prevent its being pulled out of the soil. Therefore all these modified contrivances ensure that the seed will bury itself. But supposing that one of these fruits falls upon a sheep's back. Then an exactly similar process will go on. The seed will be forced through the skin into the body of the sheep. In fact, if it should fall above any soft or vulnerable part of the animal, the sheep will very likely be killed. As a matter of fact, sheep are said to be killed by these grasses in all those four countries, distant though they are from one another. We have endeavoured in this chapter to give some faint notion of the hundreds and thousands of ingenious contrivances utilized by plants in order to ensure the dispersal and future prosperity of their children. Every species is always trying to colonize new ground, to seek fresh fields and new pastures. Plants are not content to keep to the old habitats, but every species tries to scatter its pioneers over all the neighbouring country, so that, as often happens, if it is exterminated or suppressed in one locality, new generations luxuriate elsewhere. CHAPTER XXI STORY OF THE CROPS