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

by Charles Darwin

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 competitors. 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 competition. 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.