SOME REASONS FOR PLANT MIGRATION.
53. Plants are not charitable beings.--Man uses to his advantage a
large number of plants, but there appears to be no evidence that the
schemes for their dispersion were designed for anything except to
benefit the plants themselves. The elegant foliage and beautiful
flowers, the great diversity of attractive seeds and fruits, all
point to plants as strictly selfish beings, if I may so use the term;
and not to plants as works of charity, to be devoured by animals
without any compensation. By fertilizing flowers, by distributing
plants, and by other helpful acts, animals pay for at least a portion
of the damage they do.
By an almost infinite number of devices, we have seen that seeds and
fruits flee from the parental spot on the wings of the wind, float
on currents of ocean, lake, and river. They are shot by bursting pods
and capsules in every direction. With hooks, barbs, and glands they
cling to the covering of animals. Allured by brilliant colors, birds
and other animals seek and devour the fruits of many plants, the seeds
of which are preserved from harm by a solid armor; these seeds are
then sown broadcast over the land, ready to start new colonies. Nuts
are often carried by squirrels for long distances, and there securely
buried, a few in a place. By a slow process, which, however, covers
a considerable space, in a few years many plants send forth roots,
rootstalks, stolons, and runners, and thus increase their
possessions or find new homes.
54. Plants migrate to improve their condition.--The various devices
by which plants are shifted from place to place are not merely to
extend and multiply the species, and reach a fertile soil, but to
enable them to flee from the great number of their own kind, and from
their enemies among animals and parasitic plants. The adventurers
among plants often meet with the best success, not because the seeds
are larger, or stronger, or better, but because they find, for a time,
more congenial surroundings. We must not overlook the fact, so well
established, that one of the greatest points to be gained by plant
migration is to enable different stocks of a species to be cross
fertilized, and thereby improved in vigor and productiveness.
55. Fruit grown in a new country is often fair.--Every horticulturist
knows that apples grown in a new country, that is suited to them,
are healthy and fair; but, sooner or later, the scab, and codling
moth, and bitter rot, and bark louse arrive, each to begin its
particular mode of attack. Peach trees in new places, remote from
others, are often easily grown and free from dangers; but soon will
arrive the yellows, borers, leaf curl, rot, and other enemies. For
a few years plums may be grown, in certain new localities, without
danger from curculio, or rot, or shot-hole fungus. It has long been
known that the nicest way to grow a few cabbages, radishes, squashes,
cucumbers, or potatoes is to plant a few here and there in good soil,
at considerable distances from where any have heretofore been grown.
For a time enemies are not likely to find them. I have often noticed
that, while pear-blight decimated or swept large portions of a pear
orchard, a few isolated trees, scattered about the neighborhood,
usually remain healthy. The virgin soil of the Dakotas produced, at
a trifling cost, healthy, clean wheat, but it was not long before
the Russian thistle, false flax, and other pests followed, to contest
their rights to the soil.
As animals starve out, in certain seasons when food is scarce, or
more likely migrate to regions which can afford food, so plants desert
worn-out land and seek fresh fields. As animals retreat to secluded
and isolated spots to escape their enemies, so, likewise, many plants
accomplish the same thing by sending out scouts in all directions
to find the best places; these scouts, it is needless to say, are
seeds, and when they have found a good place, they occupy it, without
waiting for further instructions.
56. Much remains to be discovered.--"In this, as in other branches
of science, we have made a beginning. We have learned just enough
to perceive how little we know. Our great masters in natural history
have immortalized themselves by their discoveries, but they have not
exhausted the field; and if seeds and fruits cannot vie with flowers
in the brilliance and color with which they decorate our gardens and
our fields, still they surely rival them--it would be impossible to
excel them--in the almost infinite variety of the problems they
present to us, the ingenuity, the interest, and the charm of the
beautiful contrivances which they offer for our study and our
admiration."[5]
[Footnote 5: _Flowers, Fruits, and Leaves_, by Sir John Lubbock, p.
96.]
Frequent rotations seem to be the rule for many plants, when left
to themselves in a state of nature. Confining to a permanent spot
invites parasites and other enemies, and a depleted soil, while
health and vigor are secured by frequent migrations. The more we study
in detail the methods of plant dispersion, the more we shall come
to agree with a statement made by Darwin concerning the devices for
securing cross-fertilization of flowers, that they "transcend, in
an incomparable degree, the contrivances and adaptations which the
most fertile imagination of the most imaginative man could suggest
with unlimited time at his disposal."[6]
[Footnote 6: _Fertilization of Orchids_, p. 351.]
Let no reader think that the topics here taken up are treated
exhaustively, for if he will go over any part of this work and verify
any observation or experiment, he will be sure to find something new,
and very likely something different from what is here stated.
BIBLIOGRAPHY.
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