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 fiber 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 vigor 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.