On Molecular and Microscopic Science, Volume 1 (of 2)Somerville, Mary
History
On Molecular and Microscopic Science, Volume 1 (of 2)
Somerville, Mary
Matter -- Constitution; Microscopy; Natural history
The Orchis pyramidalis is considered by Mr. Darwin to be the most highly
organized species of the British Orchids he has examined. It has sharp
leaves, and a close pyramid of white or rose-coloured blossoms. The
upper sepal and the two upper petals form a hood, protecting the anther
and stigmatic surfaces from the weather. In fig. 77, a front view of a
blossom, these are cut off as well as in fig. 78 _a_, which represents a
side view of the same blossom deprived of half the labellum, and the
upper part of the nectary, or spur. The labellum is long, with three
equal entire lobes, and is produced into an awl-shaped spur, or nectary.
It has a small ridge on each side of its narrow base to guide the
proboscides of insects to the mouth of the nectary, which, besides being
small, is partially closed by the pouch-shaped rostellum, which is
placed very low in this species, and is flanked on each side by a
distinct stigmatic rounded surface (fig. 77 _s s_). The rostellum (_r_)
is hollowed out on its under-side in the middle, and is filled with a
fluid. Instead of two little viscid discs or balls, as in the Orchis
mascula, there is but one which is saddle-shaped (figs. 78, 79),
carrying on its nearly flat top or seat, the two stalks of the pollinia,
of which the two truncated ends firmly adhere to its upper-surface.
Before the membrane of the rostellum ruptures, the saddle-shaped disc
forms part of its continuous surface. The upper membrane of the disc is
rather thick; it is lined with a layer of highly adhesive matter formed
within the rostellum.
[Illustration: Fig. 78. Orchis pyramidalis:—Side view of flower, with a
portion cut away; _a_, anther; _r_, rostellum; _l_, labellum; _n_,
nectary.]
[Illustration: Fig. 79. Disc of Orchis pyramidalis seen from above, with
one pollinium, flattened by force.]
[Illustration: Fig. 80. Pollinia of Orchis pyramidalis, attached to
saddle-shaped disc.]
[Illustration: Fig. 81. Pollinia of Orchis pyramidalis with the disc
contracted.]
[Illustration: Fig. 82. Pollinia of Orchis pyramidalis:—_a_, as
withdrawn by the insertion of a needle; _b_, as after the second
contraction.]
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