In my experiments with
Digitalis purpurea, some flowers on a wild plant were self-fertilised,
and others were crossed with pollen from another plant growing within
two or three feet's distance. The crossed and self-fertilised plants
raised from the seeds thus obtained, produced flower-stems in number as
100 to 47, and in average height as 100 to 70. Therefore the cross
between these two plants was highly beneficial; but how could their
sexual elements have been differentiated by exposure to different
conditions? If the progenitors of the two plants had lived on the same
spot during the last score of generations, and had never been crossed
with any plant beyond the distance of a few feet, in all probability
their offspring would have been reduced to the same state as some of the
plants in my experiments,--such as the intercrossed plants of the ninth
generation of Ipomoea,--or the self-fertilised plants of the eighth
generation of Mimulus,--or the offspring from flowers on the same
plant,--and in this case a cross between the two plants of Digitalis
would have done no good. But seeds are often widely dispersed by natural
means, and one of the above two plants or one of their ancestors may
have come from a distance, from a more shady or sunny, dry or moist
place, or from a different kind of soil containing other organic or
inorganic matter. We know from the admirable researches of Messrs.
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