1. Ipomoea purpurea.
Plants growing in the same pots, and subjected in each generation to the
same conditions, were intercrossed for nine consecutive generations.
These intercrossed plants thus became in the later generations 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 thus raised. Other flowers on the same intercrossed
plants were fertilised with pollen from another intercrossed plant,
producing seedlings of the tenth intercrossed generation. These two sets
of seedlings were grown in competition with one another, and 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 plants raised from the cross with a fresh
stock were also greatly superior in fertility to the intercrossed,
namely, in the ratio 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 having been left to be naturally fertilised. It should be
especially observed that none of the plants of either lot were the
product of self-fertilisation.
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