[1] Cf. note on p. 171.

[2] It has been found convenient to denote the various generations resulting from a cross by the signs F₁, F₂, F₃, etc. F₁ on this system denotes the first filial generation, F₂ the second filial generation produced by two parents belonging to the F₁ 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, December 16, 1910.

[9] Paradisus Terrestris, London, 1629, p. 261.