" 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, etc., 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, "reproduced itself as perfectly as if it
had been a natural species from the mountains of Chile." I have taken
some pains to ascertain the degree of fertility of some of the complex
crosses of Rhododendrons, and I am assured that many of them are
perfectly fertile.
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