at first as viscid as ever it will
become, and the nectar lying all ready for rapid suction, be accidental,
it is a fortunate accident for the plant. If not accidental, and I
cannot believe it to be accidental, what a singular case of adaptation!"
("Fertilisation of Orchids" (1st edition), page 53.)

Among exotic orchids Catasetum is particularly remarkable. One and the
same species bears different forms of flowers. The species known as
Catasetum tridentatum has pollinia with very large viscid discs;
on touching one of the two filaments (antennae) which occur on the
gynostemium of the flower the pollinia are shot out to a fairly long
distance (as far as 1 metre) and in such manner that they alight on the
back of the insect, where they are held. The antennae have, moreover,
acquired an importance, from the point of view of the physiology of
stimulation, as stimulus-perceiving organs. Darwin had shown that it is
only a touch on the antennae that causes the explosion, while contact,
blows, wounding, etc. on other places produce no effect. This form of
flower proved to be the male. The second form, formerly regarded as
a distinct species and named Monachanthus viridis, is shown to be the
female flower. The anthers have only rudimentary pollinia and do not
open; there are no antennae, but on the other hand numerous seeds
are produced. Another type of flower, known as Myanthus barbatus, was
regarded by Darwin as a third form: this was afterwards recognised
by Rolfe (Rolfe, R.A. "On the sexual forms of Catasetum with special
reference to the researches of Darwin and others," "Journ. Linn. Soc."
Vol. XXVII. (Botany), 1891, pages 206-225.) as the male flower
of another species, Catasetum barbatum Link, an identification in
accordance with the discovery made by Cruger in Trinidad that it always
remains sterile.

Darwin had noticed that the flowers of Catasetum do not secrete nectar,
and he conjectured that in place of it the insects gnaw a tissue in
the cavity of the labellum which has a "slightly sweet, pleasant and
nutritious taste." This conjecture as well as other conclusions drawn by
Darwin from Catasetum have been confirmed by Cruger--assuredly the best
proof of the acumen with which the wonderful floral structure of this
"most remarkable of the Orchids" was interpretated far from its native
habitat.

As is shown by what we have said about Catasetum, other problems in
addition to those concerned with fertilisation are de