143
Recessive characters, 19
Repulsion between factors, 90
Reversion, 59, 165
in rabbits, 59
in sweet peas, 62
in fowls, 65
in pigeons, 65
Rose comb, 33

Saunders, E. R., 54, 122
Seeds, nature of, 4
Segregation, 22
Selection, 162
Sheep, horns in, 76
Silky fowls, 30, 105
Single comb, 32
Species, nature of, 150
Species, origin of, 11
Speckled wood butterfly, 132
Spermatozoa, 3
Sports, 147
Staples-Browne, R., 66
Sterility, 151
Sterility in sweet peas, 93
Stocks, double, 122
Stocks, hoariness in, 54
Sweet pea, colour in, 44, 79
history of, 82
inheritance of hood in, 89
inheritance of size in, 62

Telegony, 167
Thrum-eye in primulas, 55
Toe, extra toe in poultry, 76
Tschermak, E., 29

Unit-character, definition of, 31

Variation, 14, 137, 139

Walnut comb, 33
Weismann, A., 13
Wheat, beard in, 74
experiments with, 157
White, dominant in poultry, 72
Wilson, J., 168

Yellow mice, 119

Zygotes, nature of, 5

* * * * *

Notes

* * * * *

[1] Cf. note on p. 171.

[2] It has been found convenient to denote the various generations
resulting from a cross by the signs F_1, F_2, F_3, etc. F_1 on this system
denotes the first filial generation, F_2 the second filial generation
produced by two parents belonging to the F_1 generation, and so on.

[3] Hurst's original cross was between a Belgian hare and an albina Angora,
which turned out to be a masked Dutch.

[4] The Spot is an almost white bird, the colour being confined to the tail
and the characteristic spot on the head.

[5] The reader who searches florists' catalogues for these varieties will
probably experience disappointment. The sweet pea has been much "improved"
in the past few years, and it is unlikely that the modern seedsman would
list such unfashionable forms.

[6] It is to be understood that wherever a given factor is present the
plant may be homozygous or heterozygous for it without alteration in its
colour.

[7] It should be mentioned that as the shape of the pollen coat, like that
of the seed coat, is a maternal character, all the grains of any given
plant are either long or else round. The two kinds do not occur together on
the same plant.

[8] For the most recent discussion of this peculiar case the reader is
referred to Professor Castle's paper in _Science_