From that day to this, every living thing--beast, bird and insect,
tree, shrub and plant--has produced after its kind. It is a law
that runs through all animal and vegetable life. Each family in
the great world of living forms was created for a special purpose,
and was intended to remain pure and distinctive until the
termination of its mission. Whenever the family boundaries are
overstepped, the curse of nature is breathed upon the generative
functions, and the illegitimate product dies out, or subsides into
hopeless degeneration. The mule is a monster, and has no progeny.

A plant, or a tree, never forgets itself. Cheat it of its root,
and the stem remains faithful. The minutest twig, put out to nurse
upon the arm of a foreign mother, feels the thrill of the great
primal law in its filmiest fibre, and breathes in every expression
of its life its fidelity. If you will walk with me into the
garden, I will show you a mountain-ash in full bloom; but on the
top of it you will see a strange little cluster of pear-blossoms.
A twig from a Seckel pear-tree was, two or three years since,
engrafted there. It had a hard time in uniting its being to that
of the alien ash, but it loved life, and so, at length, it
consented to join itself to the transplanted forest tree. It was
weak and alone, but it kept its law. Spring bathed the ash with
its own peculiar bloom, and autumn hung it with its clusters of
scarlet berries, and it was hidden from sight by the redundant
foliage, but it kept its law. The roots of the mountain-ash,
blindly reaching in the ground and imbibing its juices, knew
nothing of the little orphaned twig above, that waited for its
food; but they could not cheat it of its law. Up to a certain
point of a certain bough the rising fluids came under the law of
the mountain-ash, and there they found a gateway, guarded by an