Close-up View of the
by Brian Johnston (Canada)
Earth laughs in flowers.
The unusual perennial studied in
this article belongs to the family Campanulaceae,
which also includes the bluebell, bellflower, and lobelia. Native
to Northeastern Asia, (China, Eastern Siberia, Korea, and Japan), it
has several alternative names: Chinese Bellflower, Japanese Bellflower,
and Common Balloon Flower.
The word balloon refers to the
buds, which prior to blooming, swell to form (mostly) hollow,
pillow-shaped structures. Although the family name translates to
‘bell’, when fully opened, the flower more closely resembles a star.
‘Sentimental Blue’ is a dwarf hybrid which grows to about 15
centimetres in height, and possesses 4 centimetre diameter purple
flowers. These flowers can be seen in the image above, and in the
one that follows. Notice the deep purple radial and subsidiary
veins that decorate the fused petals.
Prior to blooming (anthesis), the petals-to-be are
greenish-white in colour, and are joined at their margins. At
this early stage, the ‘balloon’ shows little signs of the inflation
that is imminent. Notice the pointed green sepals, (modified
leaves), that ring the unopened flower’s base.
Soon however, the bud begins to
swell, and five, pointed protuberances appear at the end-points of the
lines where the petals are temporarily joined.
As time passes, further inflation
occurs, and a hint of the final purple colouration begins to appear.
The colour continues to deepen as
the bud matures.
Strangely, in the occasional bud,
the distinctive protuberances that ring the bud, point inward, rather
than outward. This bud is about to open, as revealed by its deep
purple colour, and the partial detachment of one of the petal tips from
the rest (left image).
Viewed from above, the petal tip
that has begun to separate is more obvious.
Ralph Waldo Emerson,
Perhaps it would be interesting to
take a look inside an unopened bud. In the images that follow, a
couple of petals have been removed to reveal a bud’s interior.
The buds of most flowers are densely packed structures. Not here
however! There is a great deal of air inside this
“balloon”. Both views below show the five, inward facing, yellow anthers, (male pollen producing
structures), and their blue supporting filaments. In the
scientific terminology of botany, the anthers are referred to as being ‘introrse and weakly connivent around the style’.
Now that certainly tells us a lot! If you look up the word
introrse, it means ‘dehiscing
towards the centre of the flower’. Clearer and clearer! If
you look up dehiscing, it means ‘opening’. As I said earlier in
the paragraph, the anthers are inward facing. Isn’t terminology
wonderful! Finally, the term connivent refers to the fact that
the anthers come into contact with the style that they surround, but
are not attached to it.
A view from above shows the
immature pistil of the flower, which at this early stage, consists only
of the style. The pollen
accepting stigma has yet to
In the two views that follow, one
of the anthers (and its supporting filament) has been removed to show
the style. Notice how densely hairy it is. Also note that
there are furrows at its tip that will later open, (after the flower
has bloomed), to allow the egress of the stigma.
The image below shows the blue,
flattened base of one of the filaments.
Over a period of several hours, a
bud blooms, revealing the temporary bell-shape of the flower.
Finally, the actinomorphic, 5-merous nature of the balloon
flower appears. Sorry, but I couldn’t resist the didactic
urge! Actinomorphic means ‘star-shaped’. Or, if you wish, a
shape that can be divided into symmetrical halves along any
diameter. The strange term 5-merous refers to the flower’s parts
being in groups of five – five petals, five stamens, five stigma lobes,
A closer view of a mature flower
shows that the yellow stamens are still in contact with the style that
As can be seen below, the
flower’s anthers have begun to shed pollen grains which have adhered to
the fine hairs on the style’s strikingly blue surface.
In the higher magnification image
that follows, the roughly spherical shape of these pollen grains is
Under the microscope, the stubby,
pointed hairs that cover the style’s surface can be seen clearly.
If you take a close look at the
following image, you can see that a change has occurred. The five
anthers that were earlier in contact with the style have spread apart,
and now rest on the surface of the flower’s petals.
A photomicrograph showing the
cellular structure of a petal, and one of its purple veins, follows.
The two images below show the newly
revealed surface of the style. It is liberally coated with pollen
Notice that each anther is
connected to the ‘bump’ at the flower’s centre by its flattened
filament. Also note the triangular blue ‘flaps’ in the upper
right corner of the image on the right.
These blue flaps can be seen more
clearly in the image that follows. Notice the light coloured
hairs that grow between the gaps. Beneath these flaps is the
annular nectary disk which
contains the fluid so prized by insects.
The two photomicrographs that
follow show the outer, non pollen producing, and inner, pollen
producing surfaces of an anther.
As was mentioned earlier, Balloon
Flower pollen is roughly spherical in shape.
A higher magnification
photomicrograph reveals some of the surface detail.
Close examination of the flower in
the image below reveals a significant development. The stigma has
Notice in the following images,
that the stigma is five-lobed, and that the newly exposed receptive
surfaces have practically no pollen adhering to them, while the
non-receptive back surfaces are abundantly coated. The Balloon
Flower is protandrous; its
male reproductive organs (the anthers), mature before the female
reproductive organ (the stigma). This retarded development of the
stigma helps to discourage pollination of a flower by its own pollen (a
genetically less desirable outcome). Protandry therefore,
diminishes self-pollination. Ideally, a visiting insect, while
obtaining nectar from a flower’s nectary disk, will transfer pollen
from another flower of the
same species to the receptive surface of the stigma. As a
back-up, in case this doesn’t happen, the stigma lobes curl back in
order that their receptive surfaces come in contact with the pollen on
the style. This may
result in self-pollination – a process sometimes referred to as ‘selfing’.
The two higher magnification images
below show the stigma in side and top views.
Finally, two photomicrographs
showing the cellular structure of a Balloon Flower’s leaf can be seen
Robert Fortune (1812 – 1880)
collected Platycodon grandiflorus
plants along China’s coast in 1843 for the RHS garden in Chiswick U.K.
(near London). Their extreme popularity has resulted in the
plant’s dissemination worldwide over the past hundred plus years.
The low magnification, (to 1:1),
macro-photographs were taken using a 13 megapixel Canon 5D full frame
DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.
An 8 megapixel Canon 20D DSLR,
equipped with a specialized high magnification (1x to 5x) Canon macro
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the
The photomicrographs were taken
using 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
September 2009 edition of Micscape.
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