[27] ‘The Poultry Book,’ by W. B. Tegetmeier, 1866, p. 58.
[28] ‘Gardener’s Chronicle,’ 1852, p. 765.
[29] Spooner, in ‘Journal Royal Agricult. Soc.,’ vol. xx., part ii.
[30] See Colin’s ‘Traité de Phys. Comp. des Animaux Domestiques,’ tom. ii. p. 536, where this subject is well treated.
[31] ‘Les Pigeons,’ p. 37.
[32] Vol. i., 1854, p. 101.
[33] ‘Cottage Gardener,’ 1856, p. 110.
[34] ‘Bastarderzeugung,’ s. 553.
CHAPTER XVI.
CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES—INFLUENCE OF DOMESTICATION ON FERTILITY.
DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED. VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL PREFERENCE—VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED—VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, RENDERED IN SOME DEGREE MUTUALLY STERILE—DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES WHEN CROSSED—ON THE INCREASED FERTILITY OF UNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION.