. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 182 GENETICS IN RELATION TO AGRICULTURE two varieties of tobacco of the species Nicotiana longiflora. The smaller of these two varieties has a tube length of about 40 mm., whereas the contrasted variety bears flowers the tube length of which is over twice as great, namely about 93 mm. The two varieties had been self-fertil- ized for a number of generations preceding hybricUzation, and since it can be demonstrated that continuous self-fertilization tends to reduce a variety to a homozygous condition
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 182 GENETICS IN RELATION TO AGRICULTURE two varieties of tobacco of the species Nicotiana longiflora. The smaller of these two varieties has a tube length of about 40 mm., whereas the contrasted variety bears flowers the tube length of which is over twice as great, namely about 93 mm. The two varieties had been self-fertil- ized for a number of generations preceding hybricUzation, and since it can be demonstrated that continuous self-fertilization tends to reduce a variety to a homozygous condition, it is fair to conclude that the parents represented varieties homozygous for nearly, if not quite, all their fac- tors. We are not surprised, there- fore, to find that they display only a slight variability in flower size. This shght variability is to be con- sidered merely an evidence of the influence of external conditions and of inherent variability in character expression and not of internal heterozygosity, for there is a limit below which it is apparently im- possible to force the reduction in variability of any given character. In this case the accompanying table which has been reproduced from East in its entirety will serve as the material for the following discussion. It will be seen in Table XXXIII that when the two varieties were crossed the Fi distribution occupied a position midway between the two parents. The number of plants grown was somewhat larger than that for the parents, consequently the range covered by the Fi distribution is slightly greater, but calcula- tions of the coefficient of variability show that the variability of the Fi is only slightly and not significantly greater than that of the smaller flowered parent. When we look at the F^ from such a cross, we find that although it, like the Fi, occupies an intermediate position, the range has been doubled and this in spite of the fact that the population contained only a few more individuals than that
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