The self-fertilised plants which grew in a long row
in the open ground were also remarkable for their uniformity in height,
as were the intercrossed plants in a less degree, both lots being
compared with a large number of plants raised at the same time under
similar conditions from the self-fertilised plants of the fourth
generation crossed by a fresh stock. I regret that I did not attend to
the uniformity in height of the self-fertilised seedlings in the later
generations of the other species.
These few cases seem to me to possess much interest. We learn from them
that new and slight shades of colour may be quickly and firmly fixed,
independently of any selection, if the conditions are kept as nearly
uniform as is possible, and no intercrossing be permitted. With Mimulus,
not only a grotesque style of colouring, but a larger corolla and
increased height of the whole plant were thus fixed; whereas with most
plants which have been long cultivated for the flower-garden, no
character is more variable than that of colour, excepting perhaps that
of height. From the consideration of these cases we may infer that the
variability of cultivated plants in the above respects is due, firstly,
to their being subjected to somewhat diversified conditions, and,
secondly, to their being often intercrossed, as would follow from the
free access of insects. I do not see how this inference can be avoided,
as when the above plants were cultivated for several generations under
closely similar conditions, and were intercrossed in each generation,
the colour of their flowers tended in some degree to change and to
become uniform.
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