me
other genera, which can be far more easily fertilised by the pollen of
another and distinct species, than by their own pollen; and all the
individuals of nearly all the species of Hippeastrum seem to be in this
predicament. For these plants have been found to yield seed to the pollen
of a distinct species, though quite sterile with their own pollen,
notwithstanding that their own pollen was found to be perfectly good, for
it fertilised distinct species. So that certain individual plants and all
the individuals of certain species can actually be hybridised much more
readily than they can be self-fertilised! For instance, a bulb of
Hippeastrum aulicum produced four flowers; three were fertilised by Herbert
with their own pollen, and the fourth was subsequently fertilised by the
pollen of a compound hybrid descended from three other and distinct {251}
species: the result was that "the ovaries of the three first flowers soon
ceased to grow, and after a few days perished entirely, whereas the pod
impregnated by the pollen of the hybrid made vigorous growth and rapid
progress to maturity, and bore good seed, which vegetated freely." In a
letter to me, in 1839, Mr. Herbert told me that he had then tried the
experiment during five years, and he continued to try it during several
subsequent years, and always with the same result. This result has, also,
been confirmed by other observers in the case of Hippeastrum with its
sub-genera, and in the case of some other genera, as Lobelia, Passiflora
and Verbascum. Although the plants in these experiments appeared perfectly
healthy, and although both the ovules and pollen of the same flower were
perfectly good with respect to other species, yet as they were functionally
imperfect in their mutual self-action, we must infer that the plants were
in an unnatural state. Nevertheless these facts show on what slight and
mysterious causes the lesser or greater fertility of species when crossed,
in comparison with the same species when self-fertilised, sometimes
depends.

The practical experiments of horticulturists, though not made with
scientific precision, deserve some notice. It is notorious in how
complicated a manner the species of Pelargonium, Fuchsia, Calceolaria,
Petunia, Rhododendron, &c., have been crossed, yet many of these hybrids
seed freely. For instance, Herbert asserts that a hybrid from Calceolaria
integrifolia and plantaginea, species most widely dissimilar in general
habit