Both lots of seeds, after germinating on bare sand, were planted in pairs on the opposite sides of two pots. All the remaining seeds were sown crowded on opposite sides of a third pot; but as all the self-fertilised seedlings in this latter pot died before they grew to any considerable height, they were not measured. The plants in Pots 1 and 2 were measured when between 7 and 8 inches in height, and the crossed exceeded the self-fertilised in average height by 1.57 inches. When fully grown they were again measured to the summits of their flower-heads, with the following result:--

TABLE 4/31. Iberis umbellata.

Heights of plants to the summits of their flower-heads, in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants of the Third Generation.

Pot 1 : 18 : 19. Pot 1 : 21 : 21. Pot 1 : 18 2/8 : 19 4/8.

Pot 2 : 19 : 16 6/8. Pot 2 : 18 4/8 : 7 4/8. Pot 2 : 17 6/8 : 14 4/8. Pot 2 : 21 3/8 : 16 4/8.

Total : 133.88 : 114.75.

The average height of the seven crossed plants is here 19.12 inches, and that of the seven self-fertilised plants 16.39, or as 100 to 86. But as the plants on the self-fertilised side grew very unequally, this ratio cannot be fully trusted, and is probably too high. In both pots a crossed plant flowered before any one of the self-fertilised. These plants were left uncovered in the greenhouse; but from being too much crowded they were not very productive. The seeds from all seven plants of both lots were counted; the crossed produced 206, and the self-fertilised 154; or as 100 to 75.

CROSS BY A FRESH STOCK.

From the doubts caused by the two first trials, in which it was not known with certainty that the plants had been crossed; and from the crossed plants in the last experiment having been put into competition with plants self-fertilised for three generations, which moreover grew very unequally, I resolved to repeat the trial on a larger scale, and in a rather different manner. I obtained seeds of the same crimson variety of Iberis umbellata from another nursery garden, and raised plants from them. Some of these plants were allowed to fertilise themselves spontaneously under a net; others were crossed by pollen taken from plants raised from seed sent me by Dr. Durando from Algiers, where the parent-plants had been cultivated for some generations. These latter plants differed in having pale pink instead of crimson flowers, but in no other respect. That the cross had been effective (though the flowers on the crimson mother-plant had NOT been castrated) was well shown when the thirty crossed seedlings flowered, for twenty-four of them produced pale pink flowers, exactly like those of their father; the six others having crimson flowers exactly like those of their mother and like those of all the self-fertilised seedlings. This case offers a good instance of a result which not rarely follows from crossing varieties having differently coloured flowers; namely, that the colours do not blend, but resemble perfectly those either of the father or mother plant. The seeds of both lots, after germinating on sand, were planted on opposite sides of eight pots. When fully grown, the plants were measured to the summits of the flower-heads, as shown in Table 4/32.

TABLE 4/32. Iberis umbellata.

Height of Plants to the summits of the flower-heads, measured in inches: 0 signifies that the Plant died.

Column 1: Number (Name) of Pot.

Column 2: Plants from a Cross with a fresh Stock.

Column 3: Plants from Spontaneously Self-fertilised Seeds.

Pot 1 : 18 6/8 : 17 3/8. Pot 1 : 17 5/8 : 16 7/8. Pot 1 : 17 6/8 : 13 1/8. Pot 1 : 20 1/8 : 15 3/8.

Pot 2 : 20 2/8 : 0. Pot 2 : 15 7/8 : 16 6/8. Pot 2 : 17 : 15 2/8.

Pot 3 : 19 2/8 : 13 6/8. Pot 3 : 18 1/8 : 14 2/8. Pot 3 : 15 2/8 : 13 4/8.

Pot 4 : 17 1/8 : 16 4/8. Pot 4 : 18 7/8 : 14 4/8. Pot 4 : 17 5/8 : 16. Pot 4 : 15 6/8 : 15 3/8. Pot 4 : 14 4/8 : 14 7/8.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 53

19th Century English Literature

Charles Darwin

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Charles Darwin

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