In a tropical forest also, the creepers, though they damage the trees, yet manage to find space for their leaves and flowers: more vegetable matter is formed per square yard of ground than would be the case if there were no climbing plants.
CHAPTER XXVI
PLANTS WHICH PREY ON PLANTS
The kinds of cannibals—Bacteria—Spring flowers—Pale, ghostly Wood-flowers—Their alliance with fungi—Gooseberries growing on trees—Orchid-hunting—The life of an orchid—The mistletoe—Balder the Beautiful—Druids—Mistletoe as a remedy—Its parasitic roots—The trees it prefers—The Cactus Loranthus—Yellow Rattle and Eyebright, or Milk-thief, and their root-suckers—Broomrape and toothwort—Their colour and tastes—The scales of the toothwort which catch animalcula—Sir Stamford Raffles—A flower a yard across—The Dodder—Its twining stem and sucker-roots—Parasites rare, degenerate and dangerously situated.
THE word cannibal is often used in a very loose and unscientific way. Amongst some savage tribes it is the custom to eat old people and young children; but this is only in seasons of famine and scarcity, when there is no other food available, and not because they are specially fond of them. But amongst other tribes wars are made for the special purpose of capturing fat young people to cook. Sometimes they have become so accustomed to such delicacies that they are unable to get their food in any other way. Of course, when tribes become "pure cannibals" of this last type they have to be destroyed like wild beasts.
Among plants we find all sorts of transitions and degrees of cannibalism. There are plants which sometimes, and, as it were, accidentally, attack others. But there are also real cannibal plants which live entirely on the life-juices and sap of other plants, and cannot exist by their own labours at all. Moreover, we can find almost every conceivable state of transition. These can be clearly and definitely traced from those plants which depend on the labour of their own roots and leaves to others which have no leaves, and which consist merely of one large flower and a large adhesive sucker fixed on some one else's root.
The difficulty is very often to know where to draw the line. Probably no flowering plant is quite independent of the labour and work of its neighbours. As we have tried to show in another chapter, a long preliminary cultivation by bacteria, lichens, and mosses is required before flowering plants can develop on bare rock. That is also necessary in all cases where the soil is mineral or inorganic, without any organic dust or fragments of vegetable or animal matter. Bacteria must always begin the work by preparing nitrates and other salts.
So that only those bacteria which weather rocks can be called really free and independent. But other bacteria, such as those which cause typhoid, anthrax, hydrophobia, etc., are the best possible examples of pure cannibals, or, as they are usually described, parasites.
This last word is derived from a peculiar class of people in ancient classical times, who used to appear whenever a meal was going to begin, and received food without giving anything in return. They are represented by our tramps or by the "sundowners" in Australia, who appear as soon as the evening meal is ready and when there is no possibility of going any further on their journey.
The way in which plants became parasites or cannibals is a very interesting part of plant life, and we shall try to trace some of the various stages.