It should be observed that many plants still possess a high
power of self-fertilisation, although their flowers are excellently
constructed for cross-fertilisation--for instance, those of many
papilionaceous species.
It may be admitted as almost certain that some structures, such as a
narrow elongated nectary, or a long tubular corolla, have been developed
in order that certain kinds of insects alone should obtain the nectar.
These insects would thus find a store of nectar preserved from the
attacks of other insects; and they would thus be led to visit frequently
such flowers and to carry pollen from one to the other. (10/24. See the
interesting discussion on this subject by Hermann Muller, 'Die
Befruchtung' etc. page 431.) It might perhaps have been expected that
plants having their flowers thus peculiarly constructed would profit in
a greater degree by being crossed, than ordinary or simple flowers; but
this does not seem to hold good. Thus Tropaeolum minus has a long
nectary and an irregular corolla, whilst Limnanthes douglasii has a
regular flower and no proper nectary, yet the crossed seedlings of both
species are to the self-fertilised in height as 100 to 79. Salvia
coccinea has an irregular corolla, with a curious apparatus by which
insects depress the stamens, while the flowers of Ipomoea are regular;
and the crossed seedlings of the former are in height to the
self-fertilised as 100 to 76, whilst those of the Ipomoea are as 100 to
77.
Pages:
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545