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

by Charles Darwin

The eight crossed plants were to the eight self-fertilised in height as 100 to 107. This number of plants, considering the care with which they were raised and compared, ought to have given a trustworthy result. But from some unknown cause they grew very unequally, and they became so unhealthy that only three of the crossed and three of the self-fertilised plants set any seeds, and these few in number. Under these circumstances the mean height of neither lot can be trusted, and the experiment is valueless. The cross-fertilised flowers on the parent-plants yielded rather more seeds than the self-fertilised flowers.

14. Thunbergia alata.

The six crossed plants were to the six self-fertilised in height as 100 to 108. Here the self-fertilised plants seem to have a decided advantage; but both lots grew unequally, some of the plants in both being more than twice as tall as others. The parent-plants also were in an odd semi-sterile condition. Under these circumstances the superiority of the self-fertilised plants cannot be fully trusted.

15. Nolana prostrata.

The five crossed plants were to the five self-fertilised in height as 100 to 105; so that the latter seem here to have a small but decided advantage. On the other hand, the flowers on the parent-plants which were cross-fertilised produced very many more capsules than the self-fertilised flowers, in the ratio of 100 to 21; and the seeds which the former contained were heavier than an equal number from the self-fertilised capsules in the ratio of 100 to 82.

16. Hibiscus africanus.

Only four pairs were raised, and the crossed were to the self-fertilised in height as 100 to 109. Excepting that too few plants were measured, I know of nothing else to cause distrust in the result. The cross-fertilised flowers on the parent-plants were, on the other hand, rather more productive than the self-fertilised flowers.

17. Apium petroselinum.

A few plants (number not recorded) derived from flowers believed to have been crossed by insects and a few self-fertilised plants were grown on the opposite sides of four pots. They attained to a nearly equal height, the crossed having a very slight advantage.

18. Vandellia nummularifolia.