The intercrossed plants are here to the self-fertilised in height as 100 to 92; whereas in the analogous experiment given in Table 3/19 the intercrossed plants from the self-fertilised plants of the sixth generation were inferior in height to the self-fertilised plants in the ratio of 100 to 110. I doubt whether this discordance in the results of the two experiments can be explained by the self-fertilised plants in the present case having been raised from spontaneously self-fertilised seeds, whereas in the former case they were raised from artificially self-fertilised seeds; nor by the present plants having been self-fertilised during two additional generations, though this is a more probable explanation.

With respect to fertility, the twenty-eight Chelsea-crossed plants produced 272 capsules; the twenty-seven intercrossed plants produced 24; and the seventeen self-fertilised plants 17 capsules. All the plants were left uncovered so as to be naturally fertilised, and empty capsules were rejected.

Therefore 20 Chelsea-crossed plants would have produced 194.29 capsules.

Therefore 20 Intercrossed plants would have produced 17.77 capsules.

Therefore 20 Self-fertilised plants would have produced 20.00 capsules.

The seeds contained in 8 capsules from the Chelsea-crossed plants weighed 1.1 grains.

The seeds contained in 8 capsules from the Intercrossed plants weighed 0.51 grains.

The seeds contained in 8 capsules from the Self-fertilised plants weighed 0.33 grains.

If we combine the number of capsules produced together with the average weight of contained seeds, we get the following extraordinary ratios:

Weight of seed produced by the same number of Chelsea-crossed and intercrossed plants as 100 to 4.

Weight of seed produced by the same number of Chelsea-crossed and self-fertilised plants as 100 to 3.

Weight of seeds produced by the same number of intercrossed and self-fertilised plants as 100 to 73.

It is also a remarkable fact that the Chelsea-crossed plants exceeded the two other lots in hardiness, as greatly as they did in height, luxuriance, and fertility. In the early autumn most of the pots were bedded out in the open ground; and this always injures plants which have been long kept in a warm greenhouse. All three lots consequently suffered greatly, but the Chelsea-crossed plants much less than the other two lots. On the 3rd of October the Chelsea-crossed plants began to flower again, and continued to do so for some time; whilst not a single flower was produced by the plants of the other two lots, the stems of which were cut almost down to the ground and seemed half dead. Early in December there was a sharp frost, and the stems of Chelsea-crossed were now cut down; but on the 23rd of December they began to shoot up again from the roots, whilst all the plants of the other two lots were quite dead.

Although several of the self-fertilised seeds, from which the plants in the right hand column in Table 3/20 were raised, germinated (and were of course rejected) before any of those of the other two lots, yet in only one of the ten pots did a self-fertilised plant flower before the Chelsea-crossed or the intercrossed plants growing in the same pots. The plants of these two latter lots flowered at the same time, though the Chelsea-crossed grew so much taller and more vigorously than the intercrossed.

As already stated, the flowers of the plants originally raised from the Chelsea seeds were yellow; and it deserves notice that every one of the twenty-eight seedlings raised from the tall white variety fertilised, without being castrated, with pollen from the Chelsea plants, produced yellow flowers; and this shows how prepotent this colour, which is the natural one of the species, is over the white colour.

THE EFFECTS ON THE OFFSPRING OF INTERCROSSING FLOWERS ON THE SAME PLANT, INSTEAD OF CROSSING DISTINCT INDIVIDUALS.

In all the foregoing experiments the crossed plants were the product of a cross between distinct plants. I now selected a very vigorous plant in Table 3/20, raised by fertilising a plant of the eighth self-fertilised generation with pollen from the Chelsea stock.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 38

19th Century English Literature

Charles Darwin

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