ings from the Taymouth Castle plant were found to be not
only sterile with their own pollen, but with each other's pollen, and
with the pollen of distinct species. Pollen from the Taymouth plant
failed to fertilise certain plants of the same species, but was
successful on one plant in the Edinburgh Botanic Gardens. Seedlings
were raised from this latter union, and some of their flowers were
fertilised by Mr. Munro with their own pollen; but they were found to
be as self-impotent as the mother-plant had always proved, except when
fertilised by the grafted Taymouth plant, and except, as we shall see,
when fertilised by her own seedlings. For Mr. Munro fertilised eighteen
flowers on the self-impotent mother-plant with pollen from these her
own self-impotent seedlings, and obtained, remarkable as the fact is,
eighteen fine capsules full of excellent seed! I have met with no case
in regard to plants which shows so well as this of _P. alata_, on what
small and mysterious causes complete fertility or complete sterility
depends.

The facts hitherto given relate to the much-lessened or completely
destroyed fertility of pure species when impregnated with their own pollen,
in comparison with their fertility when impregnated by distinct individuals
or distinct species; but closely analogous facts have been observed with
hybrids.

Herbert states[317] that having in flower at the same time nine hybrid
Hippeastrums, of complicated origin, descended from several species, he
found that "almost every flower touched with pollen from another cross
produced seed abundantly, and those which were touched with their own
pollen either failed entirely, or formed slowly a pod of inferior size,
with fewer seeds." In the 'Horticultural Journal' he adds that, "the
admission of the pollen of another cross-bred Hippeastrum (however
complicated the cross) to any _one_ flower of the number, is almost
sure to check the fructification of the others." In a letter written to
me in 1839, Dr. Herbert says that he had already tried these
experiments during five consecutive years, and he subsequently repeated
them, with the same invariable result. {139} He was thus led to make an
analogous trial on a pure species, namely, on the _Hippeastrum
aulicum_, which he had lately imported from Brazil: this bulb produced
four flowers, three of which wer