The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 33

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 30 : 20 4/8.

Pot 2 : 34 4/8 : 27 4/8.

Pot 3 : 34 : 28 4/8.

Pot 3 : 30 4/8 : 27 4/8.

Pot 3 : 25 : 26.

Total : 154 : 130.

The five tallest crossed plants here average 30.8, and the five tallest self-fertilised 26 inches in height, or as 100 to 84.

Three capsules were obtained by crossing flowers on the above crossed plants, and three other capsules by again self-fertilising flowers on the self-fertilised plants. One of the latter capsules appeared as fine as any one of the crossed capsules; but the other two contained many imperfect seeds. From these two lots of seeds the plants of the following generation were raised.

CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.

As in the last generation, many of the self-fertilised seeds germinated before the crossed.

Seeds in an equal state of germination were planted on the opposite sides of three pots. The crossed seedlings soon greatly exceeded in height the self-fertilised. In Pot 1, when the tallest crossed plant was 10 1/2 inches high, the tallest self-fertilised was only 3 1/2 inches; in Pot 2 the excess in height of the crossed was not quite so great. The plants were treated as in the last generation, and when fully grown measured as before. In Pot 3 both the crossed plants were killed at an early age by some animal, so that the self-fertilised had no compet.i.tors. Nevertheless these two self-fertilised plants were measured, and are included in Table 6/77. The crossed plants flowered long before their self-fertilised opponents in Pots 1 and 2, and before those growing separately in Pot 3.

TABLE 6/77. Petunia violacea (Second generation).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 57 2/8 : 13 4/8.

Pot 1 : 36 2/8 : 8.

Pot 2 : 44 4/8 : 33 2/8.

Pot 2 : 24 : 28.

Pot 3 : 0 : 46 2/8.

Pot 3 : 0 : 28 4/8.

Total : 162.0 : 157.5.

The four crossed plants average 40.5, and the six self-fertilised 26.25 inches in height; or as 100 to 65. But this great inequality is in part accidental, owing to some of the self-fertilised plants being very short, and to one of the crossed being very tall.

Twelve flowers on these crossed plants were again crossed, and eleven capsules were produced; of these, five were poor and six good; the latter contained by weight 3.75 grains of seeds. Twelve flowers on the self-fertilised plants were again fertilised with their own pollen and produced no less than twelve capsules, and the six finest of these contained by weight 2.57 grains of seeds. It should however be observed that these latter capsules were produced by the plants in Pot 3, which were not exposed to any compet.i.tion. The seeds in the six fine crossed capsules to those in the six finest self-fertilised capsules were in weight as 100 to 68. From these seeds the plants of the next generation were raised.

CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.

TABLE 6/78. Petunia violacea (third generation; plants very young).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 1 4/8 : 5 6/8.

Pot 1 : 1 : 4 4/8.

Pot 2 : 5 7/8 : 8 3/8.

Pot 2 : 5 6/8 : 6 7/8.

Pot 3 : 4 : 5 5/8.

Pot 4 : 1 4/8 : 5 3/8.

Total : 19.63 : 36.50.

The above seeds were placed on sand, and after germinating were planted in pairs on the opposite sides of four pots; and all the remaining seeds were thickly sown on the two sides of a fifth large pot. The result was surprising, for the self-fertilised seedlings very early in life beat the crossed, and at one time were nearly double their height. At first the case appeared like that of Mimulus, in which after the third generation a tall and highly self-fertile variety appeared. But as in the two succeeding generations the crossed plants resumed their former superiority over the self-fertilised, the case must be looked at as an anomaly. The sole conjecture which I can form is that the crossed seeds had not been sufficiently ripened, and thus produced weakly plants, as occurred with Iberis. When the crossed plants were between 3 and 4 inches in height, the six finest in four of the pots were measured to the summits of their stems, and at the same time the six finest of the self-fertilised plants. The measurements are given in Table 6/78, and it may be here seen that all the self-fertilised plants exceed their opponents in height, whereas when subsequently measured the excess of the self-fertilised depended chiefly on the unusual tallness of two of the plants in Pot 2. The crossed plants here average 3.27, and the self-fertilised 6.08 inches in height; or as 100 to 186.

When fully grown they were again measured, as follows:--

TABLE 6/79. Petunia violacea (third generation; plants fully grown).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 41 4/8 : 40 6/8.

Pot 1 : 48 : 39.

Pot 1 : 36 : 48.

Pot 2 : 36 : 47.

Pot 2 : 21 : 80 2/8.

Pot 2 : 36 2/8 : 86 2/8.

Pot 3 : 52 : 46.

Pot 4 : 57 : 43 6/8.

Total : 327.75 : 431.00.