In other orchids the threads cohere at one
end of the pollen-masses; and this forms the first or nascent trace of a
caudicle. That this is the origin of the caudicle, even when of
considerable length and highly developed, we have good evidence in the
aborted pollen-grains which can sometimes be detected embedded within the
central and solid parts.
With respect to the second chief peculiarity, namely, the little mass of
viscid matter attached to the end of the caudicle, a long series of
gradations can be specified, each of plain service to the plant. In most
flowers belonging to other orders the stigma secretes a little viscid
matter. Now, in certain orchids similar viscid matter is secreted, but in
much larger quantities by one alone of the three stigmas; and this stigma,
perhaps in consequence of the copious secretion, is rendered sterile. When
an insect visits a flower of this kind, it rubs off some of the viscid
matter, and thus at the same time drags away some of the pollen-grains.
>From this simple condition, which differs but little from that of a
multitude of common flowers, there are endless gradations--to species in
which the pollen-mass terminates in a very short, free caudicle--to others
in which the caudicle becomes firmly attached to the viscid matter, with
the sterile stigma itself much modified. In this latter case we have a
pollinium in its most highly developed and perfect condition.
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