44Exhibit C 109—ni.
C 110
C 111an extensive use of it with the view to the cultivation of certain here
ditary characteristics.
We show in Table C 110, after de Chapeaurouge, the pedigree
of Eelvidere, an animal which, in spite of close inbreeding, was
distinguished by excellent qualities, and by whom, out of his own
daughter, another sire of the highest rank was produced.
After long-continued and very close inbreeding, even with a faultless
condition of the germ plasm, the decrease of vitality and fertility
of the progeny asserts itself. Important evidence for this is given by
Georg. H. Shull in his exhibition of cross-fertilized, self-fertilized
and hybridized maize (Exhibit No. C 111). Shull makes the
following comments : <! Results of inbreeding with maize—crossing
between different races or genotypes, if not too distantly related,
results in a progeny which excels its parents in vitality, whereas
crosses between individuals belonging to the same genotype engender
no increase of vitality as compared with the parents.”
In maize, and presumably in most other plants and animals
in which cross-fertilization is the rule, all individuals are usually
complicated hybrids between different varieties of genotype. They
owe their vigorous constitution to this hybrid nature.
“ The result of self-fertilization or of close inbreeding is that
the hybrid nature diminishes in degree. The stock is reduced to a
homozygotic condition, and is thus deprived of the stimulus which
lies in the hybrid condition.”
“ When two given genotypes are crossed, the first hybrid genera
tion is possessed of the greatest vigour. Even the second generation
shows much less vitality, and this decrease continues with the third
and later generations. But each succeeding generation differs less
from its predecessor than the latter differed from its own parents.
As soon as the stock has become a pure line, inbreeding produces no
further weakening. ’ ’
“ The top row of the exhibited collection of maize cobs (large
cobs with many grains) is derived from a family in which for five
generations self-fertilization has been prevented by using mixed
pollen. These conditions approach those prevailing in an ordinary
field.” “ The middle row of maize cobs (small cobs with few grains)
comes from families of the same derivation as the first row; but for
five generations they have been self-fertilized. Each one has char
acters which the others do not possess. They are almost pure bred,
and continued self-fertilization produces no further adverse influence.
The cob, quite to the right, without grains, has pistils so short that
