Darwin has truly said, “The oaks are driving the pines to the sands.”  Wherever the oak is established—­and we have seen that it is already established whereever it can endure the soil and climate—­there it will remain and keep on advancing.  The oak produces comparatively few seeds.  Where it produces a hundred, the ash and maple will yield a thousand, the elm ten thousand, and many other trees a hundred thousand.  The acorn has no provision for protection and transportation like many tree seeds.  Many kinds are furnished with wings to float them on the water and carry them in the air.  Nearly every tree seed, except the acorn, has a case to protect it while growing, either opening and casting the seeds off to a distance when ripe or falling with them to protect them till they begin to germinate.  Even the equally large seeds of other kinds are protected in some way.  The hickory nut has a hard shell, which shell itself is protected by a strong covering until ripe.  The black walnut has both a hard shell and a fleshy covering.  The acorn is the only seed I can think of which is left by nature to take care of itself.  It matures without protection, falls heavily and helplessly to the ground, to be eaten and trodden on by animals, yet the few which escape and those which are trodden under are well able to compete in the race for life.  While the elm and maple seeds are drying up on the surface, the hickories and the walnuts waiting to be cracked, the acorn is at work with its coat off.  It drives its tap root into the earth in spite of grass, and brush, and litter.  No matter if it is shaded by forest trees so that the sun cannot penetrate, it will manage to make a short stem and a few leaves the first season, enough to keep life in the root, which will drill in deeper and deeper.  When age or accident removes the tree which has overshadowed it, then it will assert itself.  Fires may run over the land, destroying almost everything else, the oak will be killed to the ground, but it will throw up a new shoot the next spring, the root will keep enlarging, and when the opportunity arrives it will make a vigorous growth, in proportion to the strength of the root, and throw out strong side roots, and after that care no more for its tap root, which has been its only support, than the frog cares for the tail of the tadpole after it has got on its own legs.

There is no mystery about the succession of forest growths, nothing in nature is more plain and simple.  We cannot but admire her wisdom, economy, and justness, compensating in another direction for any disadvantage a species may have to labor under.  Every kind of tree has an interesting history in itself.  Seeds with a hard shell, or with a pulpy or resinous covering which retards their germination, are often saved from becoming extinct by these means.