The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 24

Pot 1 : 22 3/8 : 25 5/8.

Pot 1 : 19 6/8 : 12 4/8.

Pot 2 : 15 : 19 6/8.

Pot 2 : 12 2/8 : 22 3/8.

Pot 3 : 30 5/8 : 19 4/8.

Pot 3 : 18 4/8 : 7 4/8.

Pot 4 : 38 : 9 1/8.

Total : 156.50 : 116.38.

When the two lots of seedlings were between 4 and 5 inches in height they were equal, excepting in Pot 4, in which the crossed plant was much the tallest. When between 11 and 14 inches in height, they were measured to the tips of their uppermost leaves; the crossed averaged 13.46, and the self-fertilised 11.07 inches in height, or as 100 to 82. Five months later they were again measured in the same manner, and the results are given in Table 5/49.

The seven crossed plants now averaged 22.35, and the seven self-fertilised 16.62 inches in height, or as 100 to 74. But from the great inequality of the several plants, the result is less trustworthy than in most other cases. In Pot 2 the two self-fertilised plants always had an advantage, except whilst quite young over the two crossed plants.

As I wished to ascertain how these plants would behave during a second growth, they were cut down close to the ground whilst growing freely.

The crossed plants now showed their superiority in another way, for only one out of the seven was killed by the operation, whilst three of the self-fertilised plants never recovered. There was, therefore, no use in keeping any of the plants excepting those in Pots 1 and 3; and in the following year the crossed plants in these two pots showed during their second growth nearly the same relative superiority over the self-fertilised plants as before.

Tropaeolum minus.

The flowers are proterandrous, and are manifestly adapted for cross-fertilisation by insects, as shown by Sprengel and Delpino. Twelve flowers on some plants growing out of doors were crossed with pollen from a distinct plant and produced eleven capsules, containing altogether twenty-four good seeds. Eighteen flowers were fertilised with their own pollen and produced only eleven capsules, containing twenty-two good seeds; so that a much larger proportion of the crossed than of the self-fertilised flowers produced capsules, and the crossed capsules contained rather more seed than the self-fertilised in the ratio of 100 to 92. The seeds from the self-fertilised capsules were however the heavier of the two, in the ratio of 100 to 87.

Seeds in an equal state of germination were planted on the opposite sides of four pots, but only the two tallest plants on each side of each pot were measured to the tops of their stems. The pots were placed in the greenhouse, and the plants trained up sticks, so that they ascended to an unusual height. In three of the pots the crossed plants flowered first, but in the fourth at the same time with the self-fertilised. When the seedlings were between 6 and 7 inches in height, the crossed began to show a slight advantage over their opponents. When grown to a considerable height the eight tallest crossed plants averaged 44.43, and the eight tallest self-fertilised plants 37.34 inches, or as 100 to 84.

When their growth was completed they were again measured, as shown in Table 5/50.

TABLE 5/50. Tropaeolum minus.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 65 : 31.

Pot 1 : 50 : 45.

Pot 2 : 69 : 42.

Pot 2 : 35 : 45.

Pot 3 : 70 : 50 4/8.

Pot 3 : 59 4/8 : 55 4/8.

Pot 4 : 61 4/8 : 37 4/8.

Pot 4 : 57 4/8 : 61 4/8.

Total : 467.5 : 368.0.

The eight tallest crossed plants now averaged 58.43, and the eight tallest self-fertilised plants 46 inches in height, or as 100 to 79.

There was also a great difference in the fertility of the two lots which were left uncovered in the greenhouse. On the 17th of September the capsules from all the plants were gathered, and the seeds counted. The crossed plants yielded 243, whilst the same number of self-fertilised plants yielded only 155 seeds, or as 100 to 64.

Limnanthes douglasii.

Several flowers were crossed and self-fertilised in the usual manner, but there was no marked difference in the number of seeds which they yielded. A vast number of spontaneously self-fertilised capsules were also produced under the net. Seedlings were raised in five pots from the above seeds, and when the crossed were about 3 inches in height they showed a slight advantage over the self-fertilised. When double this height, the sixteen crossed and sixteen self-fertilised plants were measured to the tips of their leaves; the former averaged 7.3 inches, and the self-fertilised 6.07 inches in height, or as 100 to 83. In all the pots, excepting 4, a crossed plant flowered before any one of the self-fertilised plants. The plants, when fully grown, were again measured to the summits of their ripe capsules, with the result in Table 5/51.

TABLE 5/51. Limnanthes douglasii.

Heights of plants to the summits of their ripe capsules, measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 17 7/8 : 15 1/8.

Pot 1 : 17 6/8 : 16 4/8.

Pot 1 : 13 : 11.

Pot 2 : 20 : 14 4/8.

Pot 2 : 22 : 15 6/8.

Pot 2 : 21 : 16 1/8.

Pot 2 : 18 4/8 : 17.

Pot 3 : 15 6/8 : 11 4/8.

Pot 3 : 17 2/8 : 10 4/8.

Pot 3 : 14 : 0.

Pot 4 : 20 4/8 : 13 4/8.

Pot 4 : 14 : 13.

Pot 4 : 18 : 12 2/8.

Pot 5 : 17 : 14 2/8.

Pot 5 : 18 5/8 : 14 1/8.

Pot 5 : 14 2/8 : 12 5/8.

Total : 279.50 : 207.75.

The sixteen crossed plants now averaged 17.46, and the fifteen (for one had died) self-fertilised plants 13.85 inches in height, or as 100 to 79. Mr. Galton considers that a higher ratio would be fairer, namely, 100 to 76. He made a graphical representation of the above measurements, and adds the words "very good" to the curvature thus formed. Both lots of plants produced an abundance of seed-capsules, and, as far as could be judged by the eye, there was no difference in their fertility.]

14. LEGUMINOSAE.

In this family I experimented on the following six genera, Lupinus, Phaseolus, Lathyrus, Pisum, Sarothamnus, and Ononis.

[Lupinus luteus. (5/2. The structure of the flowers of this plant, and their manner of fertilisation, have been described by H. Muller 'Befruchtung' etc. page 243. The flowers do not secrete free nectar, and bees generally visit them for their pollen. Mr. Farrer, however, remarks 'Nature' 1872 page 499, that "there is a cavity at the back and base of the vexillum, in which I have not been able to find nectar. But the bees, which constantly visit these flowers, certainly go to this cavity for what they want, and not to the staminal tube.")