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Nicholl

Chapter 7

(1) Ipomoea purpurea Plants growing in the same pots & subjected in each generation to the same conditions had been intercrossed for from nine consecutive generations. These intercrossed plants were thus became in the later generation more or less closely inter-related. Flowers on the plants of the ninth intercrossed generation were fertilised with pollen taken from a fresh stock, and seedlings were thus raised. Other flowers on the same intercrossed plants were fertilised with pollen from another intercrossed plant, producing seedlings of the tenth intercrossed generations

These two sets of seedlings were grown in competition with each one another & differed greatly in height and fertility. For the offspring from the cross with a fresh stock exceeded in height the intercrossed plants in the ratio of 100 to 78; and this is nearly the same excess which the intercrossed had over the self-fertilised plants in all ten generations taken together, namely as 100 to 77. The offspring plants raised from the cross with a fresh stock was were also greatly superior in fertility so the intercrossed, namely in the ration of 100 to 51, as judged by the relative weight of the seed-capsules produced by an equal number of plants of the two sets, both being having been kept to be naturally fertilised. It should be especially observed