The art of caring for _trees_ is called arboriculture, and one who devotes himself to it an arborist. The art of producing and developing tree communities, or _forests_, is silviculture or forestry. HOW TREES LIVE AND GROW The intimate study of trees is full of interest. The sap, consisting of raw food material gathered by the root hairs from the soil, courses upward, through the newer wood cells of trunk and branch, to the leaves; there, under the action of sunlight, it is assimilated with carbon dioxide, and, so prepared as tree food, passes downward through the newer bark. Thus, the process never entirely suspended, even in winter, but varying in vigor with the seasons, the tree grows in stature by producing new shoots each year. No part of a tree that has concluded a season's growth is ever elongated, but remains fixed, and length is added to its terminal by the development of new buds. This is why a branch always remains at the height at which it started. On account of this fact the age of a tree or branch may be determined by counting back from the terminal one year for each section of development. On most deciduous trees this is hard to follow for more than a few years, but on the evergreens, which produce their branches in whorls, it is easy. On the other hand, diameter growth may continue indefinitely and is exhibited on any cross-section in a series of annual rings. A count of these rings will give the age of the tree at that point. Other interesting things to know are the means by which trees support themselves upright, even in severe storms; how they support the weight of heavy branches; and how the various species differ in the form, color, texture of their bark. Then the flowers and fruits. Few people know that the early spring awakening of the silver maple is marked by the appearance of its flowers weeks before the leaves come out, or that pines and oaks have flowers at all. And so with the fruits: willows produce catkins; chestnuts, burs; elms, samaras; spruce, cones. KNOWING THE TREES And then one who is fond of trees will not be satisfied until he can recognize and name at least the commoner kinds. This is field work for many seasons, for the variations as well as the fixed characters must be observed, and there are at least a hundred species to be found in New Jersey. The student will soon want a handbook like Collins and Preston's "Key to Trees," but without that he will distinguish the two great groups--evergreen and deciduous. The evergreens are also called conifers because the fruit of most of them is a cone. Almost all are ornamental but none is suitable for the street. Their wood is commonly called soft, though that of many species is quite hard, and forms the great bulk of coarse lumber used for building, etc.