Hayes and Garber - Cucurbit Breeding

120 BREEDING CROP PLANTS
Briefly, it consisted of growing and harvesting a 100-plant plot
from each plant. Selection was continued the following year.
The selections of most promise were increased and given extensive
trials by farmers. By this method new forms of superior
value were discovered.
The pure-line method of breeding self-fertilized crops was
independently discovered and later adopted (1891) by the Svalof
experiment station in Sweden. The director of the station, H.
Nilsson, was led to its adoption by the accidental discovery that
only those plots planted with seed coming from a single plant
exhibited uniformity (Newman, 1912). DeVries (1907) says:
"To this accidental circumstance, combined with the exact scientific
method of keeping extensive records, the discovery of the cause of
the diversity of the cultures was due. For precisely those cultures
which were derived from one ear only were found to be pure and uniform,
all others offering to the eye a more or less motley assemblage of forms/'
The fact that many of the agricultural varieties grown in
Sweden at the present time are the result of this method of breeding
is sufficient evidence of its success.
In addition to individual plant selection, the older mass
selection is sometimes used with self-fertilized crops. Mass
selection is the selection of a group of individuals which seem to
embody the desired characters. No attempt is made to grow
the offspring of the different individuals separately and hence a
pure-line study is impossible. In spite of this fact, mass selection
sometimes has a place in correct breeding. For example, it may
be advantageous to let nature eliminate non-hardy forms of a
winter wheat variety before beginning a study
plant progenies.
SELECTION WITHIN A PURE LINE
of individual
Early in the twentieth century Johannsen (1903, 1913) began
his famous experiments with beans and barley which resulted in
the discovery of facts which led to the development of the pureline
theory. Johannsen found that selection within a pure line
was futile.
Table XIX is typical of what he obtained by selection
within each of 19 different pure lines of beans.
Since Johannsen announced his pure-line concept, several
investigators working with other crops and other characters have
verified his conclusions.