the pollen of a compound
hybrid descended from three other and distinct 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, 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.
Mr. C. Noble, for instance, informs me that he raises stocks for
grafting from a hybrid between Rhododendron Ponticum and Catawbiense,
and that this hybrid "seeds as freely as it is possible to imagine." Had
hybrids, when fairly treated, gone on decreasing in fertility in each
successive generation, as Gartner believes to be the case, the fact
would have been notorious to nurserymen. Horticulturists raise large
beds of the same hybrids, and such alone are fairly treated, for by
insect agency the several individuals o