f the facts to be given relate to Orchids, but I will
commence with a plant belonging to a widely different family.

Sixty-three flowers of _Corydalis cava_, borne on distinct plants, were
fertilised by Dr. Hildebrand[305] with pollen from other plants of the
same species; and fifty-eight capsules were obtained, including on an
average {133} 4.5 seed in each. He then fertilised sixteen flowers
produced by the same raceme, one with another, but obtained only three
capsules, one of which alone contained any good seeds, namely, two in
number. Lastly, he fertilised twenty-seven flowers, each with its own
pollen; he left also fifty-seven flowers to be spontaneously
fertilised, and this would certainly have ensued if it had been
possible, for the anthers not only touch the stigma, but the
pollen-tubes were seen by Dr. Hildebrand to penetrate it; nevertheless
these eighty-four flowers did not produce a single seed-capsule! This
whole case is highly instructive, as it shows how widely different the
action of the same pollen is, according as it is placed on the stigma
of the same flower, or on that of another flower on the same raceme, or
on that of a distinct plant.

With exotic Orchids several analogous cases have been observed, chiefly
by Mr. John Scott.[306] _Oncidium sphacelatum_ has effective pollen,
for with it Mr. Scott fertilised two distinct species; its ovules are
likewise capable of impregnation, for they were readily fertilised by
the pollen of _O. divaricatum_; nevertheless, between one and two
hundred flowers fertilised by their own pollen did not produce a single
capsule, though the stigmas were penetrated by the pollen-tubes. Mr.
Robinson Munro, of the Royal Botanic Gardens of Edinburgh, also informs
me (1864) that a hundred and twenty flowers of this same species were
fertilised by him with their own pollen, and did not produce a capsule,
but eight flowers fertilised by the pollen of _O. divaricatum_ produced
four fine capsules: again, between two and three hundred flowers of _O.
divaricatum_, fertilised by their own pollen, did not set a capsule,
but twelve flowers fertilised by _O. flexuosum_ produced eight fine
capsules: so that here we have three utterly self-impotent species,
with their male and female organs perfect, as shown by their mutual
fertilisation. In these cases ferti