Within the wonderful world of trees lies another world - that of the organisms which harbor in trees as pests and parasites. Of these there is no end in numbers or variety. New home owners are scarcely to be blamed for becoming dismayed, as they often do, upon encountering one invader after another for the first time. This writer's counsel to clients undergoing such baptism has always been: Cheer up, few kinds of attack on trees are fatal. Study of the trees' foes-learning to anticipate and counteract them - is a sporting proposition in itself. You may lose a few skirmishes, but there is a great deal that you yourself can do to win this war. Only occasionally will an owner, particularly of young trees, have to call in a tree-service task force.

The trees' invaders are from two kingdoms - the animal and the vegetable. The former are insects (and one bird) ranging from king-size larvae of the big moths down to microscopic mites, mini-wasps, and scale organisms no bigger than a pin point. The vegetable hordes are fungi, bacteria, and viruses. These are all primitive plant forms, but there is one plant parasite that is anything but primitive except in its role, assigned by mankind, as a love symbol. This is mistletoe, one of the deadliest invaders of all.

Mistletoe might well be spelled "missile toe," for its first tiny rootlets have the power to insinuate themselves into the host tree's living tissues like the fangs of a vampire. Its pallid, waxy berries, resembling seed pearls, are carried by birds and dropped into bark crevices where they germinate under protection of their own gum. Mistletoe cannot live in soil but must steal its nourishment from a host tree's sap veins.

Where it fastens on, grotesque swellings ensue and the host's deformed members writhe away from the vampire as if in horror. No amount of chopping-out short of limb amputation will eradicate the mature bushes. Fortunately for trees, and for the human kissing custom, and for Oklahoma whose State "flower" mistletoe is, the deaths it inflicts are slow and painless. Its glaucous clumps aloft even confer a macabre beauty upon the elms, hackberries, walnuts, gums, pecans, mesquites, and (rarely) oaks, which it reduces to skeletons.

Mistletoes abound from lower New Jersey to Key West, all across the South, and up the west coast into Oregon. In much of this range they are accompanied by an even more picturesque growth called Spanish Moss, a member of the pineapple family. This stringy, grayish stuff hanging from trees, making them look like shaggy Arthur Rackham wizards, is not a true parasite. It is a typical air plant, of which lichens and orchids are other examples. Air plants do not suck a tree's life-juices but can smother it to death if allowed to run rampant.

Another conspicuous parasite, this a true one, is called witches'-broom. It shows up as dense, deforming twig clumps in hackberry, larch, and honey locust. It is caused by the sting of gall mites or by spores of a mildew fungus - maybe by both. Pruning is the only cure, if there is any.

Pruning or tissue surgery can sometimes head off one other class of parasite - the canker-forming fungi. Whenever such mechanical aids are attempted they should be followed up by feeding, usually with a high-nitrogen, to help the tree quickly seal off its canker lesions with healthy new cells before remnant fungoid mycelia (thread-roots) can spread, as in animals' fibroid tumors. Getting rid of these parasites is critical if you want to have healthy trees.