CROSSED AND SELF-FERTILISED PLANTS OF THE FIFTH GENERATION.

Seeds from both lots of the fourth generation, fertilised in the usual manner, were sown on opposite sides of three pots. When the seedlings flowered, most of the self-fertilised plants were found to consist of the tall white variety. Several of the crossed plants in Pot 1 likewise belonged to this variety, as did a very few in Pots 2 and 3. The tallest crossed plant in Pot 1 was 7 inches, and the tallest self-fertilised plant on the opposite side 8 inches; in Pots 2 and 3 the tallest crossed were 4 1/2 and 5 1/2, and the tallest self-fertilised 7 and 6 1/2 inches in height; so that the average height of the tallest plants in the two lots was as 100 for the crossed to 126 for the self-fertilised; and thus we have a complete reversal of what occurred in the four previous generations. Nevertheless, in all three pots the crossed plants retained their habit of flowering before the self-fertilised. The plants were unhealthy from being crowded and from the extreme heat of the season, and were in consequence more or less sterile; but the crossed plants were somewhat less sterile than the self-fertilised plants.

CROSSED AND SELF-FERTILISED PLANTS OF THE SIXTH GENERATION.

Seeds from plants of the fifth generation crossed and self-fertilised in the usual manner were sown on opposite sides of several pots. On the self-fertilised side every single plant belonged to the tall white variety. On the crossed side some plants belonged to this variety, but the greater number approached in character to the old and shorter kinds with smaller yellowish flowers blotched with coppery brown. When the plants on both sides were from 2 to 3 inches in height they were equal, but when fully grown the self-fertilised were decidedly the tallest and finest plants, but, from want of time, they were not actually measured. In half the pots the first plant which flowered was a self-fertilised one, and in the other half a crossed one. And now another remarkable change was clearly perceived, namely, that the self-fertilised plants had become more self-fertile than the crossed. The pots were all put under a net to exclude insects, and the crossed plants produced spontaneously only fifty-five capsules, whilst the self-fertilised plants produced eighty-one capsules, or as 100 to 147. The seeds from nine capsules of both lots were placed in separate watch-glasses for comparison, and the self-fertilised appeared rather the more numerous. Besides these spontaneously self-fertilised capsules, twenty flowers on the crossed plants again crossed yielded sixteen capsules; twenty-five flowers on the self-fertilised plants again self-fertilised yielded seventeen capsules, and this is a larger proportional number of capsules than was produced by the self-fertilised flowers on the self-fertilised plants in the previous generations. The contents of ten capsules of both these lots were compared in separate watch-glasses, and the seeds from the self-fertilised appeared decidedly more numerous than those from the crossed plants.

CROSSED AND SELF-FERTILISED PLANTS OF THE SEVENTH GENERATION.

Crossed and self-fertilised seeds from the crossed and self-fertilised plants of the sixth generation were sown in the usual manner on opposite sides of three pots, and the seedlings were well and equally thinned. Every one of the self-fertilised plants (and many were raised) in this, as well as in the eighth and ninth generations, belonged to the tall white variety. Their uniformity of character, in comparison with the seedlings first raised from the purchased seed, was quite remarkable. On the other hand, the crossed plants differed much in the tints of their flowers, but not, I think, to so great a degree as those first raised. I determined this time to measure the plants on both sides carefully. The self-fertilised seedlings came up rather before the crossed, but both lots were for a time of equal height. When first measured, the average height of the six tallest crossed plants in the three pots was 7.02, and that of the six tallest self-fertilised plants 8.97 inches, or as 100 to 128.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 35

19th Century English Literature

Charles Darwin

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Charles Darwin

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