PLANT BURGLARS—READ RIGHT THROUGH BEFORE SUSPECTING YOUR TULIP BED.
Big animals kill and eat smaller ones, and they in their turn feed on others smaller still, down to the very lowest and tiniest creatures known. This every one knows. What is not so easily realized is that a similar savage struggle for existence is always going on in the vegetable as well as the animal world. Certain plants feed on others, robbing them of their sap and juices, and eventually killing their prey as surely as does the lion when he buries his sharp teeth in an antelope’s neck.
This organized robbery is most plain to the eye in a tropical forest; but even here in our islands no one can go for a country walk without seeing plenty of instances. The mistletoe, for instance. A great dull-green bunch grows flourishing profusely on the bare limb of some half-starved apple tree. If you cut them off the apple bough, you will find the roots of the parasite have sunk deep into its substance, and are drinking up the juices which the roots of the apple tree have secreted far down in the earth below.
It is curious to note how the mistletoe has fitted itself for this thieving existence. Its berries are full of a gluey sap. This, when they fall, makes them stick in the crannies of the bark of such rough-coated trees as the apple, the poplar, and, more rarely, the oak, and there each grows and begins anew to starve and strangle its host. In the ground a mistletoe seed cannot live, and soon rots away.
The “dodders,” “greater” and “common,” may be easily identified by any one with a little botanical knowledge. The former lives on thistles; the latter sucks the juices of heath and thyme.
Broom rape is another tiny burglar, fixing itself on the roots of broom and furze, and so gaining a living. The family of broom rape comprises no less than five different varieties, all of which are incorrigible sneak thieves, and have now descended so low they can exist in no other way. One lives and grows upon the roots of clover, another fastens on ivy roots and fattens on food intended for the tendrils far above.
Ivy itself is classed by many as a burglarious plant. Indeed, its loving embraces, if not checked, are apt to strangle the tree it grows on. But, on the other hand, it is not fair to put it in the same category with the plants already mentioned, for ivy only asks from a tree support, not food, and the harm it does is due to its tight embraces depriving its upholder of air and light.
But it is to hot countries you must go to see plant crime flourishing unchecked, particularly the forests of Central America. An especially cruel sinner is one well known to us by name, the India-rubber tree. Its favorite plan seems to be to start growing on the very crown of some forest giant, such as a wild fig or a Guianese ceiba[{51}] tree. There it pushes out its great, evergreen, leathery leaves, and digs its roots down into the fast-rotting substance of its host’s trunk. Soon its long, creeping rootlets descend along the outside bark of the supporting tree, and finally reach the ground. Soon nothing is left between them but a rotting shell. The murder is accomplished, and the garroter has usurped the place of its victim.
That queer air plant known as Spanish moss kills many a fine forest tree with its solemn, gray tendrils. Like ivy, it robs its host of light and air and ends by slowly smothering its victim.
Occasionally plants not burglars by nature are forced to assume that rôle. A young mountain ash may not infrequently be seen springing from the crown of an ancient oak or other tree. The seed has been dropped there by a bird and taken root.
Ferns, too, often grow in great profusion on the long, horizontal boughs of oaks over rivers and ponds. Their weight, and the moss they encourage among their roots, end by rotting their support.
More rarely a tree may actually be watched stealing its own juices. Willows, when old, are apt to become hollow, and they rot till nothing but a shell of bark is left. If this is cut, delicate rootlets will descend from the upper portion of the cut and suck nourishment from the decaying remains of the tree itself.