Several flowers on the self-fertilised grandchildren of Hero in Table 2/16 were fertilised with pollen from the same flower; and the seedlings raised from them (great-grandchildren of Hero) formed the ninth self-fertilised generation. Several other flowers were crossed with pollen from another grandchild, so that they may be considered as the offspring of brothers and sisters, and the seedlings thus raised may be called the INTERCROSSED great-grandchildren. And lastly, other flowers were fertilised with pollen from a distinct stock, and the seedlings thus raised may be called the COLCHESTER-CROSSED great-grandchildren. In my anxiety to see what the result would be, I unfortunately planted the three lots of seeds (after they had germinated on sand) in the hothouse in the middle of winter, and in consequence of this the seedlings (twenty in number of each kind) became very unhealthy, some growing only a few inches in height, and very few to their proper height. The result, therefore, cannot be fully trusted; and it would be useless to give the measurements in detail. In order to strike as fair an average as possible, I first excluded all the plants under 50 inches in height, thus rejecting all the most unhealthy plants. The six self-fertilised thus left were on an average 66.86 inches high; the eight intercrossed plants 63.2 high; and the seven Colchester-crossed 65.37 high; so that there was not much difference between the three sets, the self-fertilised plants having a slight advantage. Nor was there any great difference when only the plants under 36 inches in height were excluded. Nor again when all the plants, however much dwarfed and unhealthy, were included. In this latter case the Colchester-crossed gave the lowest average of all; and if these plants had been in any marked manner superior to the other two lots, as from my former experience I fully expected they would have been, I cannot but think that some vestige of such superiority would have been evident, notwithstanding the very unhealthy condition of most of the plants. No advantage, as far as we can judge, was derived from intercrossing two of the grandchildren of Hero, any more than when two of the children were crossed. It appears therefore that Hero and its descendants have varied from the common type, not only in acquiring great power of growth, and increased fertility when subjected to self-fertilisation, but in not profiting from a cross with a distinct stock; and this latter fact, if trustworthy, is a unique case, as far as I have observed in all my experiments.]


In Table 2/17, we see the average or mean heights of the ten successive generations of the intercrossed and self-fertilised plants, grown in competition with each other; and in the right hand column we have the ratios of the one to the other, the height of the intercrossed plants being taken at 100. In the bottom line the mean height of the seventy-three intercrossed plants is shown to be 85.84 inches, and that of the seventy-three self-fertilised plants 66.02 inches, or as 100 to 77.

TABLE 2/17. Ipomoea purpurea. Summary of measurements of the ten generations.

Heights of Plants in inches:

Column 1: Name of Generation.

Column 2: Number of Crossed Plants.

Column 3: Average Height of Crossed Plants.

Column 4: Number of Self-fertilised Plants.

Column 5: Average Height of Self-fertilised Plants.

Column 6: n in Ratio between Average Heights of Crossed and Self-fertilised Plants, expressed as 100 to n.

First generation Table 2/1 : 6 : 86.00 : 6 : 65.66 : 76.

Second generation Table 2/2 : 6 : 84.16 : 6 : 66.33 : 79.

Third generation Table 2/3 : 6 : 77.41 : 6 : 52.83 : 68.

Fourth generation Table 2/5 : 7 : 69.78 : 7 : 60.14 : 86.

Fifth generation Table 2/6 : 6 : 82.54 : 6 : 62.33 : 75.

Sixth generation Table 2/7 : 6 : 87.50 : 6 : 63.16 : 72.

Charles Darwin

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