In the concluding chapters various related points
and questions of general interest will be discussed.
Anyone not specially interested in the subject need not attempt to read
all the details (marked []); though they possess, I think, some value,
and cannot be all summarised. But I would suggest to the reader to take
as an example the experiments on Ipomoea in Chapter 2; to which may be
added those on Digitalis, Origanum, Viola, or the common cabbage, as in
all these cases the crossed plants are superior to the self-fertilised
in a marked degree, but not in quite the same manner. As instances of
self-fertilised plants being equal or superior to the crossed, the
experiments on Bartonia, Canna, and the common pea ought to be read; but
in the last case, and probably in that of Canna, the want of any
superiority in the crossed plants can be explained.
Species were selected for experiment belonging to widely distinct
families, inhabiting various countries. In some few cases several genera
belonging to the same family were tried, and these are grouped together;
but the families themselves have been arranged not in any natural order,
but in that which was the most convenient for my purpose. The
experiments have been fully given, as the results appear to me of
sufficient value to justify the details. Plants bearing hermaphrodite
flowers can be interbred more closely than is possible with bisexual
animals, and are therefore well-fitted to throw light on the nature and
extent of the good effects of crossing, and on the evil effects of close
interbreeding or self-fertilisation.
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