A Close-up View of the
by Brian Johnston (Canada)
And all the woods are alive with the murmur
and sound of Spring,
And the rose-bud breaks into pink on the
And the crocus-bed is a quivering moon of
Girdled round with the belt of an amethyst
From: Magdalen Walks
The blooming of the common crocus has long been a harbinger of spring
in cold climates. This small flowering plant, originally native
to Southern Europe and Asia, is a member of the iris family (Iridaceae). Its popularity is
so widespread that, over the years, many colourful cultivars have been
developed for the nursery trade.
One particular species, the saffron crocus (Crocus sativus), produces the
world’s most expensive spice (by weight) – saffron. The flowers’ stigmas
and styles are dried and used in cooking as a seasoning, and
colouring agent. It should be kept in mind, however, that most
varieties of crocus are extremely
poisonous! The toxic compound in the plant is called colchicine, [(S)-N-(5,6,7,9-tetrahydro-1,2,3,10-tetramethoxy-9-oxobenzo[a]
heptalen-7-yl) acetamide], and it produces symptoms similar to
arsenic poisoning. In the worst case situation, a person that has
ingested crocus tissues dies of respiratory failure.
Crocus buds have an inverted tear-drop shape formed by six petals in
two whorls of three. The outer whorl’s petals are slightly larger
than the inner whorl’s.
When a petal of the purple flower seen in the first image is examined
under the microscope, using low magnification, the surface cells appear
to be shiny, and slightly iridescent.
Higher magnification reveals details of the petal’s cellular structure.
Near the petal’s base, where it joins to the stalk, purple gives way to
The base of one of the patterned flowers is bright red, and this colour
extends to the top portion of the stalk.
The bottom of the stem growing from the plant’s bulb is wrapped in
several layers of white, cloth-like tissue. This gives each
plant’s base a very distinctive look. Note that both flower, and
leaf stems are shrouded in this wrapping.
A close-up of the tissue shows its unusual cloth-like texture.
Two photomicrographs of the tissue, shown with increasing
magnification, can be seen below.
As the buds begin to bloom, the characteristic shape of crocus flowers
Although the flowers’ petals eventually open up more than those shown
below, they tend to be less symmetrical, (and less photogenic)!
If you look carefully at the narrow leaves of the crocus, you may be
able to see a central, lighter coloured stripe on each leaf.
Under the microscope, the explanation for the lighter colour is
revealed. Cells in the centre of the leaf contain less
chlorophyll than those along the edges.
Here is the purple crocus flower after its ‘best to view before’
date. Although the petals are rather ragged, they have opened up
enough to allow the flower’s reproductive structures to be seen.
Higher magnification reveals details of the structures.
Surrounding the central style
that branches into three feathery stigmas
(female pollen accepting organs), are three anthers (pollen producing
organs). The colour differences in the two images are the result
of different cameras being used. On the left is an image taken
with the Canon 20D DSLR, and on the right is an image taken with the
Sony DSC F-828. Although the Sony tends to produce images with
more ‘punch’, the true colour is given by the Canon DSLR.
Here again, the two cameras were used to image a flower’s three stigma
A low magnification photomicrograph of the edge of one of the stigma’s
‘fronds’ can be seen below.
Higher magnification reveals the stubby, sticky protuberances that ring
the stigma’s edge. These protuberances aid in the retention of
The three anthers at the base of the flower’s style can be seen
below. They are completely encrusted with yellow pollen
grains. (The right-hand DSLR image shows the true colour.)
The right image also shows the point where the style divides to support
the three stigma lobes.
The photomicrograph on the right shows the many pollen grains that
cling to one another on the surface of an anther.
Using a higher magnification reveals that the pollen grains are roughly
spherical in shape, and that they lack noticeable surface detail.
Finally, here is an image of a new purple crocus bud erupting from its
So many crocus cultivars have been developed by botanists, that there
are actually rules to judge the desirable traits of each type in
horticultural flower shows! An excellent source of information
about the crocus can be found at the web-site mentioned in ‘further
Most of the macro-photographs were taken with an eight megapixel Canon
20D DSLR equipped with a Canon EF 100 mm f 2.8 Macro lens which focuses
to 1:1. A Canon 250D achromatic close-up lens was used to obtain
higher magnifications in several images.
A few photographs were taken with an eight megapixel Sony CyberShot
DSC-F 828 equipped with achromatic close-up lenses (Canon 250D, Nikon
5T, 6T, Sony VCL-M3358, and shorter focal length achromat) used singly
or in combination. The lenses screw into the 58 mm filter threads of
the camera lens.
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 May
2009 edition of Micscape.
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