152 On the Species of the Genus Primula in Essex.
thickly covered with short bristles or papillae. The anthers
are attached to the sides of the tube about half-way up, and
the tube enlarges itself slightly above them. They contain
pollen of an opaque nature and oblong form. A single grain
of cowslip pollen, according to Darwin's measurement,6
is 25.400μ long; according to Mr. Bennett,7 it is 25.400μ
long by 12.700μ broad; pollen from the long-styled form of
the primrose, as given by the same authority, is 22.860μ by
12.700μ, but some which Mr. Rosling has been kind enough
to measure was 25.400μ long; Mr. Rosling has also found
pollen from the same form of P. elatior to measure 22.860μ
in length by 15.240μ in breadth.
In the short-styled or "Thrum-eyed" form (fig. 1 b), the
style is only sufficiently long to support the stigma at about
half the height of the tube, or almost exactly in the same
position that is occupied by the anthers in the other form.
The stigma itself is broader, more depressed, and much
smoother. The anthers are of the same size as in the long-
styled form, but are affixed to the sides of the corolla-tube
at its top or only just within the entrance. The pollen they
contain is larger, more transparent, and almost spherical.
Some short-styled cowslip-pollen which Darwin measured
was 36.285-39.914μ long, thus comparing with the other form
as 100 to 67. According to Mr. Bennett's measurement it is
35.560μ by 25.400μ. The same authority states that pollen
from the same form of the primrose is 30.480μ by 19.050μ,
and some which Mr. Rosling measured proved to be 35.560μ
long. Mr. Rosling finds that the pollen of the short-styled
form of the oxlip is 35.560μ long by 20.320μ broad. The
pollen of these three species is seen to be much alike when
examined under the microscope, being, as Mr. Bennett says,
"shortly cylindrical rather than ellipsoid." Mr. Rosling,
Mr. Bennett, and myself have all observed that the number
of longitudinal furrows with which the grains are marked is
variable. The unfertilised ovules of the short-styled form
are smaller than those of the long-styled form.
There is no difference whatever to be observed in the two
forms as regards the leaves, root, or "habit" of the plant,
6 [We have reduced all these measurements, which were given in dis-
cordant fractions of an inch by the several observers, to micromillimetres
(= μ; 1000 μ = 1 millimetre), in accordance with the simple metric
system now adopted by the Royal Microscopical Society. It is to be
hoped that all microscopical observers will use the system, and so render
their micrometer measurements comparable one with another. It will be
adopted in the future in these 'Transactions.'—Ed.]
7 'Popular Science Review,' April, 1875, p. 113.