University of Virginia biologists who have been giving particular attention to the aphis are interested primarily in the substance injected into the leaves. It must be one of the most potent growth factors in nature. The amount any one aphid is able to inject is indescribably minute, even though some of them make as many as 50 separate injections. The material causes the leaf cells to become larger and to multiply much more rapidly until a “house” many times the size of the aphis is complete in a few days. The structure is perfect, even including a “picket fence” of tiny hairs around its base to keep out invaders.
The substance exists in such minute amounts that thus far it has been impossible to isolate it in anything approaching a pure form. The Virginia biologists have set themselves a task requiring infinite patience over many years—tracing the increase of the amount in the salivary glands of each individual through each of its fourteen lives, and also through the eggs with which the strange life cycle starts.
The present clues indicate that the substance is a filterable virus—tiniest of living things compared with which the pinhead-sized aphis is like a whale compared to a fly.
Shyness Characteristic of Giant Rats
Biggest of the extant true rats is the giant rat of Liberia. It is two feet or more in length and is similar in appearance to the Norway rat which infests houses all over the world. Fortunately this creature never has invaded the homes of men. It is a shy animal of the cane brakes.
Nocturnal Potto
One of the weirdest of living mammals is the potto—“ghost monkey”, of West African jungles. It is about the size of a squirrel, with soft, yellow fur and protruding yellow eyes which shine like malevolent witch lights in the darkness of the jungle nights. The potto is a nocturnal animal of the tree tops. Its weird, whimpering cries are believed by natives to be the voices of evil spirits. The little creature is an aberrant member of the family of lemurs, ancient offshoots of the same family from which sprang the monkeys and great apes.
Where Trees are Square
A few miles north of the Panama Canal Zone is “the valley of square trees.” This is the only known place in the world where trees have rectangular trunks. They are members of the cottonwood family. Saplings of these trees now are being grown at the University of Florida to find out if they retain their squareness in a different environment. It is believed, however, that the shape is probably due to some unknown but purely local condition. That the cause is deep-seated is indicated by the fact that the tree rings, each representing a year’s growth, also are square.