Close-up View of the Wildflower
by Brian Johnston (Canada)
One of my childhood memories is being
shown how to pinch the sides of this pretty yellow flower in order to
"open the dragon's mouth". At that time, this common weed was
referred to as a wild
snapdragon. Today, it is often called
or yellow toadflax.
This last name was given to
the plant because of the flower's supposed resemblance to a small toad,
or alternatively, the mouth of a small toad! I must admit that in
my opinion, the comparisons require a very large stretch of the
imagination. To me, the flower looks remarkably like a
hypothetical dragon's mouth! The 'flax' in the name refers to the
fact that before flowering, the stems with their long, narrow leaves
closely resemble those of flax plants.
The image above shows the top portion of a stem with its spike (or
raceme) of closely packed showy
yellow flowers. The plant is
usually ten to thirty centimetres in height and is normally found in
patches formed by the growth of perennial creeping roots.
The first image, and the one below, show the unusual shape of the
flower. There are five petals, three on the bottom that are fused
except at the tips, and two at the top that are similarly fused.
The petals together form a corolla,
(the collective term for the petals
of a flower) that has an upper and lower lip. This lower lip is
deep yellow or orange in colour. Each flower is from 1.5 to 4
centimetres in length, including the long spur at the bottom.
A side view of one flower shows the ring of five green bracts (modified
leaves) that cup the flower at its midpoint, and connect it to the
stem. The mouth of the flower is normally firmly closed, and more
strength than the average pollinating insect possesses is required to
push the bright yellow-orange base down to gain access to the
stamens. When a large bee is attracted by the bright colour of
the bottom lip of the flower, its mass pushes down the lip to partially
reveal the nectar stored in the long spur. In order to get its
proboscis into the nectar, it must push its hairy head into the open
bloom. In so doing, pollen grains from the anthers are
transferred to the bee and these are eventually carried to the stigma
of another flower resulting in cross-pollination.
(Self-pollination doesn't occur in toadflax.)
Notice in the image below, that the unopened flower bud reveals the
bottom lip of the flower's mouth.
By removing the yellow-orange bottom lip of the flower, it is possible
to see the four pollen covered anthers (the male pollen producing
organs) arranged as two pairs. In newly opened flowers, the two
anthers in each pair often appear joined. At a later stage they
A clearer view of the internal contents of the flower can be obtained
by removing both upper and lower lips. Notice that the upper
anthers have separated in this bloom. The pale greenish-white
stigma (the female pollen accepting organ) can be seen between the
lower filaments and anthers. The height of the stigma is
variable, but it usually is positioned somewhere between the two anther
Under the microscope, dark-ground illumination reveals details of one
anther and its supporting filament. Both are covered in pollen.
A higher magnification shows that many of the pollen grains seem to be
connected by fine thread-like structures.
The following photograph shows the ellipsoidal shape of toadflax pollen
At the base of the filament that supports the anther, there are
finger-like protuberances, green on the side closest to the stem, and
gray on the opposite side.
These speckled protuberances can be seen more clearly in the images
The greenish-white stigma of a toadflax flower is visible in the bottom
left corner of the following image.
Dark-ground illumination reveals the style, and the stigma itself more
Although yellow toadflax is considered a noxious weed in many areas of
North America, its charming little flowers provide a visual feast for
wildflower enthusiasts and a welcome source of nectar for many bees
from June to October!
The low magnification photographs
in the article were taken using a Nikon Coolpix 4500 with a combination
of natural light and the Nikon Cool light SL-1. Higher
magnification images were taken with natural light using a Sony
CyberShot DSC-F 717 equipped with a combination of achromatic close-up
lenses (Nikon 5T, 6T and shorter focal length achromat) which screw
into the 58 mm filter threads of the camera lens. (These produce
a magnification of from 0.5X to 9X for a 4x6 inch image.) Still
higher magnifications were obtained by using a macro coupler (which has
two male threads) to attach a reversed 50 mm focal length f 1.4 Olympus
SLR lens to the F 717. (The magnification here is about 13X for a
4x6 inch image.) The photomicrographs were taken with a Leitz SM-Pol
microscope (using a dark ground condenser), and the Coolpix 4500.
A Flower Garden of
A complete graphical index of all
of my flower articles can be found here.
The Colourful World of
A complete graphical index of all
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the March
2009 edition of Micscape.
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