THE SURVIVAL OF THE FIT
The plants that most perfectly meet their conditions are able to
persist. _They perpetuate themselves._ Their offspring are likely
to inherit some of the attributes that enabled them successfully
to meet the battle of life. _The fit_ (those best adapted to their
conditions) _tend to survive_.
Adaptation to conditions depends on the fact of variation; that is,
if plants were perfectly rigid or invariable (all exactly alike) they
could not meet new conditions. Conditions are necessarily new for
every organism. _It is impossible to picture a perfectly inflexible
and stable succession of plants or animals._
=Breeding.=—_Man is able to modify plants and animals._ All our
common domestic animals are very unlike their original ancestors.
So all our common and long-cultivated plants have varied from their
ancestors. Even in some plants that have been in cultivation less
than a century the change is marked: compare the common black-cap
raspberry with its common wild ancestor, or the cultivated blackberry
with the wild form.
[Illustration: FIG. 5.—DESIRABLE AND UNDESIRABLE TYPES OF COTTON
PLANTS. Why?]
By choosing seeds from a plant that pleases him, the breeder may be
able, under given conditions, to produce numbers of plants with
more or less of the desired qualities; from the best of these, he
may again choose; and so on until the race becomes greatly improved
(Figs. 5, 6, 7). This process of continuously choosing the most
suitable plants is known as =selection=. A somewhat similar process
proceeds in wild nature, and it is then known as =natural selection=.
[Illustration: FIG. 6.—FLAX BREEDING.
_A_ is a plant grown for seed production;
_B_ for fibre production. Why?]
[Illustration: FIG. 7.—BREEDING.
_A_, effect from breeding from smallest grains (after four years),
average head; _B_, result from breeding from the plumpest and
heaviest grains (after four years), average head.]
SUGGESTIONS.—=6.= Every pupil should undertake at least one simple
experiment in selection of seed. He may select kernels from
the best plant of corn in the field, and also from the poorest
plant,—having reference not so much to mere incidental size and
vigour of the plants that may be due to accidental conditions in
the field, as to the apparently constitutional strength and size,
number of ears, size of ears, perfectness of ears and kernels,
habit of the plant as to suckering, and the like. The seeds may
be saved and sown the next year. Every crop can no doubt be very
greatly improved by a careful process of selection extending over
a series of years. Crops are increased in yield or efficiency in
three ways: better general care; enriching the land in which they
grow; attention to breeding.