That certain plants, for instance, Viola tricolor, Digitalis purpurea,
Sarothamnus scoparius, Cyclamen persicum, etc., which have been
naturally cross-fertilised for many or all previous generations, should
suffer to an extreme degree from a single act of self-fertilisation is a
most surprising fact. Nothing of the kkind has been observed in our
domestic animals; but then we must remember that the closest possible
interbreeding with such animals, that is, between brothers and sisters,
cannot be considered as nearly so close a union as that between the
pollen and ovules of the same flower. Whether the evil from
self-fertilisation goes on increasing during successive generations is
not as yet known; but we may infer from my experiments that the increase
if any is far from rapid. After plants have been propagated by
self-fertilisation for several generations, a single cross with a fresh
stock restores their pristine vigour; and we have a strictly analogous
result with our domestic animals. (12/2. Ibid chapter 19 2nd edition
volume 2 page 159.) The good effects of cross-fertilisation are
transmitted by plants to the next generation; and judging from the
varieties of the common pea, to many succeeding generations. But this
may merely be that crossed plants of the first generation are extremely
vigorous, and transmit their vigour, like any other character, to their
successors.
Pages:
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615