The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 30

Total : 89.0 : 73.5.

The four tallest crossed plants averaged 22.25, and the four tallest self-fertilised 18.37 inches in height; or as 100 to 82. I was surprised to find that the anthers of a good many of these self-fertilised plants did not cohere and did not contain any pollen; and the anthers even of a very few of the crossed plants were in the same condition. Some flowers on the crossed plants were again crossed, four capsules being thus obtained; and some flowers on the self-fertilised plants were again self-fertilised, seven capsules being thus obtained. The seeds from both lots were weighed, and it was calculated that an equal number of capsules would have yielded seed in the proportion by weight of 100 for the crossed to 60 for the self-fertilised capsules. So that the flowers on the crossed plants again crossed were much more fertile than those on the self-fertilised plants again self-fertilised.

PLANTS OF THE SECOND GENERATION.

The above two lots of seeds were placed on damp sand, and many of the crossed seeds germinated, as on the last occasion, before the self-fertilised, and were rejected. Three or four pairs in the same state of germination were planted on the opposite sides of two pots; a single pair in a third pot; and all the remaining seeds were sown crowded in a fourth pot. When the seedlings were about one and a half inches in height, they were equal on both sides of the three first pots; but in Pot 4, in which they grew crowded and were thus exposed to severe compet.i.tion, the crossed were about a third taller than the self-fertilised. In this latter pot, when the crossed averaged 5 inches in height, the self-fertilised were about 4 inches; nor did they look nearly such fine plants. In all four pots the crossed plants flowered some days before the self-fertilised. When in full flower the tallest plant on each side was measured; but before this time the single crossed plant in Pot 3, which was taller than its antagonist, had died and was not measured. So that only the tallest plant on each side of three pots was measured, as in Table 5/69.

TABLE 5/69. Lobelia ramosa (Second Generation).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Tallest Crossed Plant in each Pot.

Column 3: Tallest Self-fertilised Plant in each Pot.

Pot 1 : 27 4/8 : 18 4/8.

Pot 2 : 21 : 19 4/8.

Pot 3 : 21 4/8 : 19.

Crowded.

Total : 70 : 57.

The average height of the three tallest crossed plants is here 23.33, and that of the tallest self-fertilised 19 inches; or as 100 to 81.

Besides this difference in height, the crossed plants were much more vigorous and more branched than the self-fertilised plants, and it is unfortunate that they were not weighed.

Lobelia fulgens.

This species offers a somewhat perplexing case. In the first generation the self-fertilised plants, though few in number, greatly exceeded the crossed in height; whilst in the second generation, when the trial was made on a much larger scale, the crossed beat the self-fertilised plants. As this species is generally propagated by off-sets, some seedlings were first raised, in order to have distinct plants. On one of these plants several flowers were fertilised with their own pollen; and as the pollen is mature and shed long before the stigma of the same flower is ready for fertilisation, it was necessary to number each flower and keep its pollen in paper with a corresponding number. By this means well-matured pollen was used for self-fertilisation. Several flowers on the same plant were crossed with pollen from a distinct individual, and to obtain this the conjoined anthers of young flowers were roughly squeezed, and as it is naturally protruded very slowly by the growth of the pistil, it is probable that the pollen used by me was hardly mature, certainly less mature than that employed for self-fertilisation. I did not at the time think of this source of error, but I now suspect that the growth of the crossed plants was thus injured. Anyhow the trial was not perfectly fair. Opposed to the belief that the pollen used in crossing was not in so good a state as that used for self-fertilisation, is the fact that a greater proportional number of the crossed than of the self-fertilised flowers produced capsules; but there was no marked difference in the amount of seed contained in the capsules of the two lots. (5/24. Gartner has shown that certain plants of Lobelia fulgens are quite sterile with pollen from the same plant, though this pollen is efficient on any other individual; but none of the plants on which I experimented, which were kept in the greenhouse, were in this peculiar condition.)

As the seeds obtained by the above two methods would not germinate when left on bare sand, they were sown on the opposite sides of four pots; but I succeeded in raising only a single pair of seedlings of the same age in each pot. The self-fertilised seedlings, when only a few inches in height, were in most of the pots taller than their opponents; and they flowered so much earlier in all the pots, that the height of the flower-stems could be fairly compared only in Pots 1 and 2.

TABLE 5/70. Lobelia fulgens (First Generation).

Heights of flower-stems measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Height of Flower-stems on the Crossed Plants.

Column 3: Height of Flower-stems on the Self-fertilised Plants.

Pot 1 : 33 : 50.

Pot 2 : 36 4/8 : 38 4/8.

Pot 3 : 21* : 43.

Pot 4 : 12* : 35 6/8.

*Not in full flower.

The mean height of the flower-stems of the two crossed plants in Pots 1 and 2 is here 34.75 inches, and that of the two self-fertilised plants in the same pots 44.25 inches; or as 100 to 127. The self-fertilised plants in Pots 3 and 4 were in every respect very much finer than the crossed plants.

I was so much surprised at this great superiority of the self-fertilised over the crossed plants, that I determined to try how they would behave in one of the pots during a second growth. The two plants, therefore, in Pot 1 were cut down, and repotted without being disturbed in a much larger pot. In the following year the self-fertilised plant showed even a greater superiority than before; for the two tallest flower-stems produced by the one crossed plant were only 29 4/8 and 30 1/8 inches in height, whereas the two tallest stems on the one self-fertilised plant were 49 4/8 and 49 6/8 inches; and this gives a ratio of 100 to 167.

Considering all the evidence, there can be no doubt that these self-fertilised plants had a great superiority over the crossed plants.

CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.

TABLE 5/71. Lobelia fulgens (Second Generation).

Heights of flower-stems measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 27 3/8 : 32 3/8.

Pot 1 : 26 : 26 3/8.

Pot 1 : 24 3/8 : 25 1/8.

Pot 1 : 24 4/8 : 26 2/8.

Pot 2 : 34 : 36 2/8.

Pot 2 : 26 6/8 : 28 6/8.

Pot 2 : 25 1/8 : 30 1/8.

Pot 2 : 26 : 32 2/8.

Pot 3 : 40 4/8 : 30 4/8.

Pot 3 : 37 5/8 : 28 2/8.

Pot 3 : 32 1/8 : 23.

Pot 4 : 34 5/8 : 29 4/8.

Pot 4 : 32 2/8 : 28 3/8.

Pot 4 : 29 3/8 : 26.

Pot 4 : 27 1/8 : 25 2/8.

Pot 5 : 28 1/8 : 29.

Pot 5 : 27 : 24 6/8.

Pot 5 : 25 3/8 : 23 2/8.

Pot 5 : 24 3/8 : 24.

Pot 6 : 33 5/8 : 44 2/8.

Pot 6 : 32 : 37 6/8.