Close-up View of the
by Brian Johnston (Canada)
Wild cucumber is known by many names,
some of which are: prickly cucumber, wild balsam apple, balsam apple,
creeping jenny, four-seeded bur cucumber and concombre grimpant.
It exists throughout North America as a trailing vine that can be up to
six metres long. The plant grows from an underground tuber that
can weigh up to 50 kilograms!
Both locations that I used to
obtain specimens, (over a two year period), were near the banks of
streams or rivers. Wild cucumber normally uses branched tendrils
to climb shrubs and trees, but some plants simply trail along the
Botanically speaking, the plant is
a member of the gourd or cucurbitaceae family. The
genus name Echinocystis
is derived from the Greek words echinos, meaning
“hedgehog” and kustis
meaning “bladder”. These terms refer to the shape of the fruit,
one of which can be seen above.
The two images below show a typical
plant. The large leaves that can be seen in the second photograph
are alternate, and attached to the stem by long stalks. Each leaf
is palmately shaped, and has five pointed lobes. At the junction
of the leaf stem and the main stem, (the leaf axil), a long string of flowers,
(called a panicle) is
attached. All but one of the flowers in a panicle are male.
The one female flower is located at the leaf axil.
As mentioned earlier, the wild
cucumber stem is supported by many curled tendrils which occur in
groups of three, and are attached opposite to each leaf axil. The
strength of these tendrils is amazing. As can be seen below, it
was sometimes easier to cut the supporting stem, when trying to pull
the wild cucumber plant away from its environment!
The tip of a single panicle, with
its many male flowers, is shown in the image that follows.
Each smaller branch emanating from
the main panicle stem holds a group of flowers. Several examples
are shown below.
The male flower is white, with a
green center, and has six petals which curve up to form a shallow bowl
shape. Most flowers are 8 to 16 mm in diameter.
At the center of the flower is a
single stamen consisting of a
green supporting filament and
yellow anther (male pollen
producing organ). If you look closely, the tip of each petal
appears to be covered in fine white hairs.
Under the microscope, (using
dark-ground illumination), the structure of a petal tip is
visible. The cells appear to be transparent, and the petal is
covered with glandular (round-tipped) protuberances.
A higher magnification reveals more
details of these protuberances. The gland at the top of the
right-hand image appears segmented.
The colour of the petals
transitions from white to green at the center of the flower.
Notice the tiny, green, needle-like sepals (modified leaves) that are
visible between the petals.
Several glandular structures can be
seen projecting from the green area.
A photomicrograph of the filament
supporting the anther reveals many ellipsoidal pollen grains with
Growing at the base of each panicle
of flowers, with its stalk attached to a leaf axil, the female flower
is distinguished by its spherical, spiked ovary. Since the ovary
is beneath the petals, it is referred to as “inferior”.
After fertilization, the ovary
begins its transformation into the fruit of the wild cucumber.
In the image on the left below, the
remnants of the single stigma,
(the female pollen accepting organ), is visible at the bottom of the
fruit. The image on the right shows the sharp prickles that
emanate from the fruit’s surface.
It is difficult not to stand and
stare when one comes upon a late-stage fruiting wild cucumber
vine. The many pendulous green ellipsoids are quite striking.
The mature fruit shown in the two
following images was about 5 cm long. The prickles are relatively
weak, and bend rather than penetrate the skin when the fruit is handled.
Two close-ups of plant structures
follow. The first image shows a corkscrew-like tendril, while the
second shows mature prickles, which have turned from green to yellow at
this late stage of development.
The longitudinal cross-section
through the fruit shows two of the four seeds. (There are two
more “behind” the two shown.) Most of the fruit is composed of
fleshy greenish-white material.
A transverse cross-section reveals
the position of all four seeds. Notice the darker outer capsule,
beige inner tissue, and empty space at the center of each seed.
About a month after the earlier
fruit had been picked and photographed, I returned to the same location
and removed several, now dried fruit shells. The outer structure
is now light brown, and an interesting inner seed-protecting webbed
structure can be seen. The right image shows that all four seeds
exit through the two oval openings in this inner protective
chamber. In fact, if you look closely, you may be able to see one
dark brown seed still in position deep within the left-hand chamber.
With much shaking, I was able to
dislodge one of the flat, oval, seeds. Normally as the shell
dries out, and begins to break apart, gravity causes the seeds to fall
to the ground.
To get a better view of the
interestingly patterned inner structure, I cut open the outer layer
with scissors. The structure is a marvel of engineering! It
is not only extremely strong, but appears to be waterproof as well!
This strange wildflower is not very
abundant in the area where I live in Toronto. When I first found
the plant, there were perhaps four or five examples growing up the
trunks of trees near a stream. One year later, during the hottest
summer on record, there was not a single plant to be found in the same
area! Since I still needed some additional photographs to
complete this article, I was forced to look elsewhere.
Fortunately, while visiting my parents who live about 100 km away, I
found a huge number of plants growing beside the river which runs
through the town. The year before there had been almost
none! Such are the vagaries of plant growth!
An eight megapixel Sony CyberShot
DSC-F 828 equipped with achromatic close-up lenses, (Nikon 5T, 6T, Sony
VCL-M3358, and shorter focal length achromat used singly or in
combination), was used to take most of the macro images. The lenses
screw into the 58 mm filter threads of the camera lens. 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 828. A few of the
photographs in the article were taken with an eight megapixel Canon 20D
DSLR and Canon EF 100 mm f 2.8 Macro lens. ( The images were
photographed over two summers.) The photomicrographs were taken
with a Leitz SM-Pol microscope (using a dark-ground condenser), and a
Nikon Coolpix 4500 camera.
The following references have been
found to be valuable in the identification of wildflowers, and they are
also a good source of information about them.
Dickinson, Timothy, et al. 2004.
The ROM Field Guide to Wildflowers of Ontario. Royal Ontario
Museum & McClelland and Stewart Ltd, Toronto, Canada.
Thieret, John W. et al. National
Audubon Society Field Guide to North American Wildflowers - Eastern
Region. 2002. Alfred A. Knopf, Inc. (Chanticleer Press, Inc. New
Kershaw, Linda. 2002. Ontario
Wildflowers. Lone Pine Publishing, Edmonton, Alberta,Canada.
Royer, France and Dickinson,
Richard. 1999. Weeds of Canada. University of Alberta
Press and Lone Pine Publishing, Edmonton, Alberta, Canada.
Crockett, Lawrence, J. 2003.
A Field Guide to Weeds (Based on Wildly Successful Plants,
1977) Sterling Publishing Company, Inc. New York, NY.
Mathews, Schuyler F.
2003. A Field Guide to Wildflowers (Adapted from Field Book
of American Wildflowers, 1902), Sterling Publishing Company, Inc.
New York, NY.
Barker, Joan. 2004. The
Encyclopedia of North American Wildflowers. Parragon Publishing,
Microscopy UK or their contributors.
Published in the
October 2006 edition of Micscape.
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