“Trees,” states Asa Gray in his famous essay on the _Longevity of Trees_, “far outlast all living things. They never die of old age, but only from injury or disease, or, in a word, from accidents. If not destroyed by accident, that is, by extrinsic causes—they do not eventually perish, like ourselves, from old age. It is commonly thought that they are fully exposed to the inevitable fate of all living things, but this springs from a false analogy which we have unconsciously established between plants and animals. This popular analogy might, perhaps, hold good if the tree were actually formed like the animal, all parts of which are created at once in their rudimentary state, and soon attain their fullest development so that the functions are carried on throughout life in the same set of organs. If this were the case of the tree it would likewise die sooner or later of old age. “But the tree is an aggregate of many individuals united in a common trunk and why should not the aggregate, the tree, last indefinitely? To establish the proper analogy, we must not compare the tree with man, but with the coral formations in which numerous individuals, engrafted and blended on a common base, conspire to build up immense coral groves which have endured for ages; the inner and older parts consisting of the untenanted cells of individuals that have long since perished, while fresh structures are continually produced on the surface. The individuals, indeed, perish; but the aggregate may endure as long as time itself. So with the tree. “Only the leaf may be said to die of old age. It lives but a single season and is the proper emblem of mortality. But the leaves are necessarily renewed every year, so are the other essential organs of the plant. It annually renews not only its buds and leaves, but its wood and its roots; everything, indeed, that is concerned with its life and growth. “Though the wood in the center and large branches—the produce of buds and leaves that had long ago disappeared—may die and decay; yet, while new individuals are formed on the surface with each successive crop of fresh buds, and placed in as favorable communication with the soil and the air as their predecessors, the aggregate, the tree, would appear to have no necessary, no inherent limit to its existence.”