ldren of Hero certainly inherit the powers of growth of their parents; for they greatly exceed in height the self-fertilised offspring of the other self-fertilised plants, and even exceed by a trifle the intercrossed plants,--all of the corresponding generation.

Several flowers on the self-fertilised children of Hero in Table 2/14 were fertilised with pollen from the same flower; and from the seeds thus produced, self-fertilised plants of the eighth generation (grandchildren of Hero) were raised. Several other flowers on the same plants were crossed with pollen from the other children of Hero. The seedlings raised from this cross may be considered as the offspring of the union of brothers and sisters. The result of the competition between these two sets of seedlings (namely self-fertilised and the offspring of brothers and sisters) is given in Table 2/16.

TABLE 2/16. Ipomoea purpurea.

Heights of Plants in inches:

Column 1: Number (Name) of Pot.

Column 2: Self-fertilised Grandchildren of Hero, from the Self-fertilised Children. Eighth Generation.

Column 3: Grandchildren from a cross between the self-fertilised children of Hero. Eighth Generation.

Pot 1 : 86 6/8 : 95 6/8. Pot 1 : 90 3/8 : 95 3/8.

Pot 2 : 96 : 85. Pot 2 : 77 2/8 : 93.

Pot 3 : 73 : 86 2/8. Pot 3 : 66 : 82 2/8. Pot 3 : 84 4/8 : 70 6/8.

Pot 4 : 88 1/8 : 66 3/8. Pot 4 : 84 : 15 4/8. Pot 4 : 36 2/8 : 38. Pot 4 : 74 : 78 3/8.

Pot 5 : 90 1/8 : 82 6/8. Pot 5 : 90 5/8 : 83 6/8.

Total : 1037.00 : 973.16.

The average height of the thirteen self-fertilised grandchildren of Hero is 79.76 inches, and that of the grandchildren from a cross between the self-fertilised children is 74.85; or as 100 to 94. But in Pot 4 one of the crossed plants grew only to a height of 15 1/2 inches; and if this plant and its opponent are struck out, as would be the fairest plan, the average height of the crossed plants exceeds only by a fraction of an inch that of the self-fertilised plants. It is therefore clear that a cross between the self-fertilised children of Hero did not produce any beneficial effect worth notice; and it is very doubtful whether this negative result can be attributed merely to the fact of brothers and sisters having been united, for the ordinary intercrossed plants of the several successive generations must often have been derived from the union of brothers and sisters (as shown in Chapter 1), and yet all of them were greatly superior to the self-fertilised plants. We are therefore driven to the suspicion, which we shall soon see strengthened, that Hero transmitted to its offspring a peculiar constitution adapted for self-fertilisation.

It would appear that the self-fertilised descendants of Hero have not only inherited from Hero a power of growth equal to that of the ordinary intercrossed plants, but have become more fertile when self-fertilised than is usual with the plants of the present species. The flowers on the self-fertilised grandchildren of Hero in Table 2.16 (the eighth generation of self-fertilised plants) were fertilised with their own pollen and produced plenty of capsules, ten of which (though this is too few a number for a safe average) contained 5.2 seeds per capsule,--a higher average than was observed in any other case with the self-fertilised plants. The anthers produced by these self-fertilised grandchildren were also as well developed and contained as much pollen as those on the intercrossed plants of the corresponding generation; whereas this was not the case with the ordinary self-fertilised plants of the later generations. Nevertheless some few of the flowers produced by the grandchildren of Hero were slightly monstrous, like those of the ordinary self-fertilised plants of the later generations. In order not to recur to the subject of fertility, I may add that twenty-one self-fertilised capsules, spontaneously produced by the great-grandchildren of Hero (forming the ninth generation of self-fertilised plants), contained on an average 4.47 seeds; and this is as high an average as the self-fertilised flowers of any generation usually yielded.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 26

19th Century English Literature

Charles Darwin

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Charles Darwin

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