The browsing line being always at nearly the same distance of about six feet from the ground, it acts as a scale, by which the eye measures the comparative height of trees at any distance; for this reason the importance of a large tree may be injured by cutting the lower branches above this usual standard. It is obvious that the foregoing trees [see fig. 65] are of different ages, characters, and heights, yet the browsing line is the same in all, and furnishes a natural scale by which we at once decide on their relative heights at various distances. Let us suppose the same trees pruned or trimmed by man, [as in fig. 66], and not by cattle, and this scale will be destroyed: thus, a full grown oak may be made to look like an orchard-tree, or by encouraging the under branches to grow lower than the usual standard, a thorn or a crab-tree may be mistaken for an oak, at a distance.