STRUCTURE OF ORCHID FLOWERS
Most people are familiar with the regular arrangement of the segments of
the flowers of Amaryllids and Lilies, with their prominent pistils and
anthers. The first stage in the advance of the Orchid family is shown in
the Apostasieae, comprising _Apostasia_, _Neuwiedia_ and _Adactylus_, in
which the perianth segments are more or less regular and the anthers in
some degree prominent, Neuwiedia, with its free stamens and prominent
style, appearing at first sight nearer to some of the Amaryllids than to
the Orchideae commonly seen in gardens.
The Cypripedieae, although so widely separated from other sections as to
suggest that in the operations of nature a vast number of connecting
types must have become extinct, is the next step, the labellum being
formed into a pouch with infolded side lobes. The column has a prominent
staminode with two fertile anthers below it, one on each side of the
column and behind the stigmatic plate. The upper sepal is frequently the
showiest feature in the flower; the lower sepals are joined and arranged
behind the lip, whilst the petals extend on each side and vary much in
form.
In gardens, the whole of the genus is known as Cypripedium, although the
South American species (Selenipedium), having a three-celled ovary,
differ widely from the one-celled East Indian and Malayan species, and
other sections have such marked and consistent botanical differences as
to warrant the botanist in separating them under different sub-generic
names. The third section of Orchidae, the largest family of the
Monocotyledons, forms the chief class of Orchids as they are known in
gardens. In this class the stamens and style unite into a column, and at
the top of the column the pollen masses are situated; these are covered
by the anther-cap, and in a cavity is the stigma with its viscid surface
to receive the pollen grains.
So diverse and intricate are the forms of the flowers, and especially
labellums, that there is little doubt that insect aid is necessary in
their natural habitats to bring about pollination. It has been proved by
the operations carried out in cross-fertilisation in gardens that no
class of plants can be so readily crossed under artificial conditions.
It is not necessary here to go further into structural details, as the
peculiarities of each section will be remarked on under their different
headings. But it may be said that in what are called abnormal flowers,
which have perfect stamens and style, can be seen instances suggesting
the evolutionary process; these would be more common but for the number
of connecting links which have dropped out in the great struggle for
existence.