The two lots were allowed to fertilise themselves spontaneously: the crossed plants produced a large number of capsules, whilst the self-fertilised produced very few and poor ones. The seeds from eight of the capsules on the crossed plants weighed .65 grain, whilst those from eight of the capsules on the self-fertilised plants weighed only .22 grain; or as 100 to 34.

The crossed plants in the above three pots, as in almost all the previous experiments, flowered before the self-fertilised. This occurred even in the third pot in which the crossed seeds were sown four days after the self-fertilised seeds.

Lastly, seeds of both lots were sown on opposite sides of a large pot in which a Fuchsia had long been growing, so that the earth was full of roots. Both lots grew miserably; but the crossed seedlings had an advantage at all times, and ultimately attained to a height of 3 1/2 inches, whilst the self-fertilised seedlings never exceeded 1 inch. The several foregoing experiments prove in a decisive manner the superiority in constitutional vigour of the crossed over the self-fertilised plants.

In the three generations now described and taken together, the average height of the ten tallest crossed plants was 8.19 inches, and that of the ten tallest self-fertilised plants 5.29 inches (the plants having been grown in small pots), or as 100 to 65.

In the next or fourth self-fertilised generation, several plants of a new and tall variety appeared, which increased in the later self-fertilised generations, owing to its great self-fertility, to the complete exclusion of the original kinds. The same variety also appeared amongst the crossed plants, but as it was not at first regarded with any particular attention, I know not how far it was used for raising the intercrossed plants; and in the later crossed generations it was rarely present. Owing to the appearance of this tall variety, the comparison of the crossed and self-fertilised plants of the fifth and succeeding generations was rendered unfair, as all the self-fertilised and only a few or none of the crossed plants consisted of it. Nevertheless, the results of the later experiments are in some respects well worth giving.

CROSSED AND SELF-FERTILISED PLANTS OF THE FOURTH GENERATION.

Seeds of the two kinds, produced in the usual way from the two sets of plants of the third generation, were sown on opposite sides of two pots (1 and 2); but the seedlings were not thinned enough and did not grow well. Many of the self-fertilised plants, especially in one of the pots, consisted of the new and tall variety above referred to, which bore large and almost white flowers marked with crimson blotches. I will call it the WHITE VARIETY. I believe that it first appeared amongst both the crossed and self-fertilised plants of the last generation; but neither my gardener nor myself could remember any such variety in the seedlings raised from the purchased seed. It must therefore have arisen either through ordinary variation, or, judging from its appearance amongst both the crossed and self-fertilised plants, more probably through reversion to a formerly existing variety.

In Pot 1 the tallest crossed plant was 8 1/2 inches, and the tallest self-fertilised 5 inches in height. In Pot 2, the tallest crossed plant was 6 1/2 inches, and the tallest self-fertilised plant, which consisted of the white variety, 7 inches in height; and this was the first instance in my experiments on Mimulus in which the tallest self-fertilised plant exceeded the tallest crossed. Nevertheless, the two tallest crossed plants taken together were to the two tallest self-fertilised plants in height as 100 to 80. As yet the crossed plants were superior to the self-fertilised in fertility; for twelve flowers on the crossed plants were crossed and yielded ten capsules, the seeds of which weighed 1.71 grain. Twenty flowers on the self-fertilised plants were self-fertilised, and produced fifteen capsules, all appearing poor; and the seeds from ten of them weighed only .68 grain, so that from an equal number of capsules the crossed seeds were to the self-fertilised in weight as 100 to 40.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 34

19th Century English Literature

Charles Darwin

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Charles Darwin

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