One self-fertilised plant in Pot 3 exceeded, and one in Pot 4 equalled in height, its opponent. The self-fertilised plants showed no sign of inheriting the precocious growth of their parents; this having been due, as it would appear, to the abnormal state of the seeds from the unhealthiness of their parents. The fourteen self-fertilised plants yielded only forty spontaneously self-fertilised capsules, to which must be added seven, the product of ten flowers artificially self-fertilised. On the other hand, the fourteen crossed plants yielded 152 spontaneously self-fertilised capsules; but thirty-six flowers on these plants were crossed (yielding thirty-three capsules), and these flowers would probably have produced about thirty spontaneously self-fertilised capsules. Therefore an equal number of the crossed and self-fertilised plants would have produced capsules in the proportion of about 182 to 47, or as 100 to 26. Another phenomenon was well pronounced in this generation, but I believe had occurred previously to a slight extent; namely, that most of the flowers on the self-fertilised plants were somewhat monstrous. The monstrosity consisted in the corolla being irregularly split so that it did not open properly, with one or two of the stamens slightly foliaceous, coloured, and firmly coherent to the corolla. I observed this monstrosity in only one flower on the crossed plants. The self-fertilised plants, if well nourished, would almost certainly, in a few more generations, have produced double flowers, for they had already become in some degree sterile. (2/1. See on this subject 'Variation of Animals and Plants under Domestication' chapter 18 2nd edition volume 2 page 152.)

TABLE 2/10. Ipomoea purpurea (Ninth Generation).

Heights of Plants in inches:

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 83 4/8 : 57. Pot 1 : 85 4/8 : 71. Pot 1 : 83 4/8 : 48 3/8.

Pot 2 : 83 2/8 : 45. Pot 2 : 64 2/8 : 43 6/8. Pot 2 : 64 3/8 : 38 4/8.

Pot 3 : 79 : 63. Pot 3 : 88 1/8 : 71. Pot 3 : 61 : 89 4/8.

Pot 4 : 82 4/8 : 82 4/8. Pot 4 : 90 : 76 1/8.

Pot 5 : 89 4/8 : 67. Pot 5 : 92 4/8 : 74 2/8. Pot 5 : 92 4/8 : 70. Crowded plants.

Total : 1139.5 : 897.0.

CROSSED AND SELF-FERTILISED PLANTS OF THE TENTH GENERATION.

Six plants were raised in the usual manner from the crossed plants of the last generation (Table 2/10) again intercrossed, and from the self-fertilised again self-fertilised. As one of the crossed plants in Pot 1 in Table 2/11 became much diseased, having crumpled leaves, and producing hardly any capsules, it and its opponent have been struck out of the table.

TABLE 2/11. Ipomoea purpurea (Tenth Generation).

Heights of Plants in inches:

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 92 3/8 : 47 2/8. Pot 1 : 94 4/8 : 34 6/8.

Pot 2 : 87 : 54 4/8. Pot 2 : 89 5/8 : 49 2/8. Pot 2 : 105 : 66 2/8.

Total : 468.5 : 252.0.

The five crossed plants average 93.7 inches, and the five self-fertilised only 50.4, or as 100 to 54. This difference, however, is so great that it must be looked at as in part accidental. The six crossed plants (the diseased one here included) yielded spontaneously 101 capsules, and the six self-fertilised plants 88, the latter being chiefly produced by one of the plants. But as the diseased plant, which yielded hardly any seed, is here included, the ratio of 101 to 88 does not fairly give the relative fertility of the two lots. The stems of the six crossed plants looked so much finer than those of the six self-fertilised plants, that after the capsules had been gathered and most of the leaves had fallen off, they were weighed. Those of the crossed plants weighed 2,693 grains, whilst those of the self-fertilised plants weighed only 1,173 grains, or as 100 to 44; but as the diseased and dwarfed crossed plant is here included, the superiority of the former in weight was really greater.]

THE EFFECTS ON THE OFFSPRING OF CROSSING DIFFERENT FLOWERS ON THE SAME PLANT, INSTEAD OF CROSSING DISTINCT INDIVIDUALS.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 22

19th Century English Literature

Charles Darwin

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