The remaining plants were left uncovered, and as pollen was carried from plant to plant by the hive and humble-bees which incessantly visit the flowers, they produced an abundance of capsules. Of the necessity of pollen being carried from one plant to another, I had ample evidence in the case of this species and of R. odorata; for those plants, which set no seeds or very few as long as they were protected from insects, became loaded with capsules immediately that they were uncovered.

Seeds from the flowers spontaneously self-fertilised under the net, and from flowers naturally crossed by the bees, were sown on opposite sides of five large pots. The seedlings were thinned as soon as they appeared above ground, so that an equal number were left on the two sides. After a time the pots were plunged into the open ground. The same number of plants of crossed and self-fertilised parentage were measured up to the summits of their flower-stems, with the result given in Table 4/35. Those which did not produce flower-stems were not measured.

TABLE 4/35. Reseda lutea, in pots.

Heights of plants to the summits of the flower-stems measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 21 : 12 7/8. Pot 1 : 14 2/8 : 16. Pot 1 : 19 1/8 : 11 7/8. Pot 1 : 7 : 15 2/8. Pot 1 : 15 1/8 : 19 1/8.

Pot 2 : 20 4/8 : 12 4/8. Pot 2 : 17 3/8 : 16 2/8. Pot 2 : 23 7/8 : 16 2/8. Pot 2 : 17 1/8 : 13 3/8. Pot 2 : 20 6/8 : 13 5/8.

Pot 3 : 16 1/8 : 14 4/8. Pot 3 : 17 6/8 : 19 4/8. Pot 3 : 16 2/8 : 20 7/8. Pot 3 : 10 : 7 7/8. Pot 3 : 10 : 17 6/8.

Pot 4 : 22 1/8 : 9. Pot 4 : 19 : 11 4/8. Pot 4 : 18 7/8 : 11. Pot 4 : 16 4/8 : 16. Pot 4 : 19 2/8 : 16 3/8.

Pot 5 : 25 2/8 : 14 6/8. Pot 5 : 22 : 16. Pot 5 : 8 6/8 : 14 3/8. Pot 5 : 14 2/8 : 14 2/8.

Total : 412.25 : 350.86.

The average height of the twenty-four crossed plants is here 17.17 inches, and that of the same number of self-fertilised plants 14.61; or as 100 to 85. Of the crossed plants all but five flowered, whilst several of the self-fertilised did not do so. The above pairs, whilst still in flower, but with some capsules already formed, were afterwards cut down and weighed. The crossed weighed 90.5 ounces; and an equal number of the self-fertilised only 19 ounces, or as 100 to 21; and this is an astonishing difference.

Seeds of the same two lots were also sown in two adjoining rows in the open ground. There were twenty crossed plants in the one row and thirty-two self-fertilised plants in the other row, so that the experiment was not quite fair; but not so unfair as it at first appears, for the plants in the same row were not crowded so much as seriously to interfere with each other's growth, and the ground was bare on the outside of both rows. These plants were better nourished than those in the pots and grew to a greater height. The eight tallest plants in each row were measured in the same manner as before, with the following result:--

TABLE 4/36. Reseda lutea, growing in the open ground.

Heights of plants to the summits of the flower-stems measured in inches.

Column 1: Crossed Plants.

Column 2: Self-fertilised Plants.

28 : 33 2/8. 27 3/8 : 23. 27 5/8 : 21 5/8. 28 6/8 : 20 4/8. 29 7/8 : 21 5/8. 26 6/8 : 22. 26 2/8 : 21 2/8. 30 1/8 : 21 7/8.

Total : 224.75 : 185.13

The average height of the crossed plants, whilst in full flower, was here 28.09, and that of the self-fertilised 23.14 inches; or as 100 to 82. It is a singular fact that the tallest plant in the two rows, was one of the self-fertilised. The self-fertilised plants had smaller and paler green leaves than the crossed. All the plants in the two rows were afterwards cut down and weighed. The twenty crossed plants weighed 65 ounces, and twenty self-fertilised (by calculation from the actual weight of the thirty-two self-fertilised plants) weighed 26.25 ounces; or as 100 to 40.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 60

19th Century English Literature

Charles Darwin

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Charles Darwin

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