genera, such as Leptotes, Cyrtopodium, and Rodriguezia!
_Oncidium crispum_, however, differs from the foregoing species in
varying much in its self-sterility; some plants producing fine pods
with their own pollen, others failing to do so; in two or three
instances, Fritz Mueller observed that the pods produced by pollen
taken from a distinct flower on the same plant, were larger than those
produced by the flower's own pollen. In _Epidendrum cinnabarinum_, an
orchid belonging to another division of the family, fine pods were
produced by the plant's own pollen, but they contained by weight only
about half as much seed as the capsules which had been fertilized by
pollen from a distinct plant, and in one instance from a distinct
species; moreover, a very large proportion, and in some cases nearly
all the seed produced by the plant's own pollen, was embryonless and
worthless. Some self-fertilized capsules of a Maxillaria were in a
similar state.

Another observation made by Fritz Mueller is highly remarkable, namely,
that with various orchids the plant's own pollen not only fails to
impregnate the flower, but acts on the stigma, and is acted on, in an
injurious or poisonous manner. This is shown by the surface of the
stigma in contact with the pollen, and by the pollen itself, becoming
in from three to five days dark brown, and then decaying. The
discolouration and decay are not caused by parasitic cryptogams, which
were observed by Fritz Mueller in only a single instance. These changes
are well shown by placing on the same stigma, at the same time, the
plant's own pollen and that from a distinct plant of the same species,
or of another species, or even of another and widely remote genus.
Thus, on the stigma of _Oncidium flexuosum_, the plant's own pollen and
that from a distinct plant were placed side by side, and in five days'
time the latter was perfectly fresh, whilst the plant's own pollen was
brown. On the other hand, when the pollen of a distinct plant of the
_Oncidium flexuosum_, and of the _Epidendrum zebra_ (_nov. spec.?_),
were placed together on the same stigma, they behaved in exactly the
same manner, the grains separating, emitting tubes, and penetrating the
stigma, so that the two {135} pollen-masses, after an interval of
eleven days, could not be distinguished except by the di