View of the
English White Oak
robus cv ‘Fastigiata'
by Brian Johnston (Canada)
Live thy Life,
Young and old,
then Fall'n at length,
Like yon oak,
Autumn-changed Look, he stands,
Bright in spring,
Trunk and bough
“The Oak” Alfred Lord
The mighty Oak is not only strong, but it also has a very long lifespan
– up to 500 or 600 years if left undisturbed! White Oak,
the subject of this article grows mainly in the Eastern part of North
America, and its wood has been used for many years to produce
furniture, floors and veneers. During the colonial period it was
much prized for ship building. White Oak is sometimes called
Stave Oak, because it makes excellent, tight-fitting barrel staves.
Quercus robus is member of the
Fagaceae, or Beech
Tree parts photographed for this article were obtained from several
young trees growing in my local park. Typically, White Oak trees
have wide, irregular crowns when they grow with lots of space around
them. In a forest situation, the crowns tend to be upright and
oval. For some reason, the park trees behave as though they are
in a forest situation! Notice in the image on the left, below,
that two of the trees are stunted, and one of them has died. For
some inexplicable reason, the park maintenance crews tend to store salt
at the bases of these two trees for dispersal onto the slippery park
road during winter. The result is not surprising! (Note
that the unusual pointed shape of these oak trees is due to the fact
that they are English
White Oak Quercus robus cv ‘Fastigiata')
Leaves are positioned alternately on the plant’s stems, and have from 7
to 10 rounded, finger-like lobes around their perimeter. Each
leaf’s upper surface is smooth, and reflected light results in the
white highlights that are visible in the left image. Notice the
complex vein structure of the tip of one of the leaves (right image).
When a species has both male and female structures growing on the same
plant, it is referred to as monoecious
(“in the same house”). The two images that follow show the very
beginnings of the English White Oak’s reproductive structures. At
base of new growth shoots (left image), red-brown male staminate catkins begin to
develop. At new growth axils,
where the leaves’ stalks meet the stem), red-brown female
pistillate catkins begin to
develop. (A catkin is a
compact cluster of unisexual flowers.)
Below, in the left image, a group of reddish bracts, (modified leaves), protects
each developing staminate catkin. Later, these groups of bracts
open at the top, and cone-shaped, or oval-shaped male catkins appear.
When the tightly packed, yellow-green, bi-lobed anthers, (male pollen
producing organs) first appear, they are so densely packed that their
supporting filaments are not visible (left image). As the
catkin’s stalk increases in length, the filaments eventually appear
In the image that follows, the anthers have not yet begun to produce
Higher magnification views of these immature anthers can be seen below.
Notice the different appearance of the catkin, once pollen production
Low, and high magnification photomicrographs follow that show an anther.
Ironically, Stave Oak pollen grains are barrel-shaped! Several
longitudinal grooves mark the surface of each.
Within a day or two, as the anthers and their filaments dry out, some
of the male catkins begin to look untidy, and they turn a light brown
colour. Other bract enclosures however, have yet to open.
robus cv ‘Fastigiata' twigs are
red-brown, or slightly gray in colour, and tend to be hairless, and
rather shiny. Notice the interesting crater-like depressions on
the twigs’ surfaces.
Most descriptions of female English White Oak flowers make the point
are not visible to the naked eye. How true! Last spring, I
made a determined attempt to find such a flower on “my” trees. I
failed completely. During a five day period in which I was unable
to visit the park, the flowers had bloomed, and those not fertilized
had fallen from the branches (abscised).
short time later however, the tiny, swollen fruit that eventually
transform into recognizable acorns, became noticeable. The two
immature acorns shown below are only 3 to 4 mm in diameter.
Each nearly spherical fruit is initially, almost completely enclosed by
a cap which is made up of many
layers of overlapping greenish bracts
(modified leaves). As the darker green fruit grows, it pushes
aside the material near the cap’s opening, increasing the opening’s
diameter. Notice in the two images, the remnants of the flower’s
style projecting from the top of the fruit.
Although the cap continues to grow, the fruit increases in size even
more quickly. This results in the original, almost spherical
acorn, taking on an ellipsoidal, or egg-shape.
Notice in the image that follows, that several tiny immature acorns
have dried up and turned brown. Also note the strangely coloured
dark brown fruit in the upper right corner of the image.
Additional images of two of these tiny “dead” acorns can be seen
below. The one shown in the image on the left still has its very
prominent green style attached.
The many layers of overlapping bracts that constitute the acorn’s cap
can be seen clearly in the high magnification macro-image that follows.
Acorns mature approximately four months after fertilization. The
acorn’s cap has reached its maximum size early on, but the fruit itself
has continued to grow to an amazing degree, forming a long, thin
Two examples of these late stage acorns can be seen below. At
this point the adhesion between cap and fruit is much weakened.
Eventually, the fruit drops out of the cap and falls to the
ground. (Sometimes squirrels pull the fruit out of the cap before
If a sharp knife is used to cut lengthwise through a fruit, it can be
seen to consist of a tough, thick, outer cover that protects its high
water content interior. (In the image, the fruit is held in
position by the wire seen at its base.)
The outer casing, and inner core of the fruit are shown below.
After the ellipsoidal fruit has fallen from the cap, the cap remains
attached to the tree for some time, and then it too falls to the ground.
The placenta-like structure that provides the connection between the
acorn’s stalk, and its fruit can be seen in the image that follows.
Oak trees grown in the open, like those in my park, may produce acorns
as early as 20 years of age. A particular tree may produce very
different numbers of acorns in successive years, and good acorn crops
occur only every 4 to 10 years. These acorns are usually
disseminated by rodents - mainly squirrels and mice. They are a
favourite food for many wildlife species.
Most 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. An
eight megapixel Sony CyberShot DSC-F 828 equipped with achromatic
close-up lenses (Canon 250D, Nikon 6T, and Sony VCL-M3358 used singly,
or in combination), was used to take a few of the images. The tree
images were taken with a five megapixel Sony DSC-F 717.
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 April
2009 edition of Micscape.
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