How slowly through the lilac-scented air
descends the tranquil moon.
………

Henry Wadsworth Longfellow
(The Spanish Student)

When lilacs last in the dooryard bloom'd
And the great star early droop'd in the western sky in the night,
I mourn'd, and yet shall mourn with ever-returning spring.
………

Walt Whitman
(Written at the death of Lincoln)

April is the cruelest month, breeding
Lilacs out of the dead land, mixing
Memory and desire, stirring
Dull roots with spring rain.
………

Spring has truly arrived when the first lilac flowers fill the air with their unmistakable scent.  This wonderful plant is usually found as a multi-stemmed shrub with an irregular, rounded outline.  Part of its usefulness to the landscaper and gardener comes from the fact that it is particularly hardy, being able to withstand severe environmental conditions.

Originating in eastern Europe, lilacs were brought to North America by pioneers in the early 1600’s.  From the beginning, their appearance and scent proved extremely popular.  So popular in fact, that during the 1800’s, plant scientists began developing hybrids (cultivars) which improved upon the lowly “common” lilac’s characteristics.  In some of these cultivars however, larger and more colourful blooms were obtained at the expense of the strength of the scent.

Modern chemistry has found that the scent associated with lilacs is due to a number of organic molecules manufactured by the plant.  The most important of these is alpha-terpineol, an organic (carbon containing) alcohol.  Historically, this compound was obtained by removing the essential oils from lilac flowers, and was used to produce scented soaps, bath preparations and household products.  This is still done today, but the alpha-terpineol is produced synthetically in the laboratory.  (The true, and synthetic molecules are identical.)  In smaller amounts, the compound may be used to formulate synthetic flavours such as nutmeg, orange, peach and other florals.

The structural formula, ball and stick model, and molecular shape of alpha-terpineol are shown below.  (HyperChem Pro was used to produce the illustrations.  A technique called geometry optimization was used to find a low energy (stable) shape.  Other stable configurations exist.)

The name lilac is derived from the Arabic word ‘layak’ and the Persian word ‘nilak’ referring to the colour blue, and from the Sanskrit word for purple.  The genus name Syringa comes from the Greek word for ‘pipe’, and refers to the tubular bottom of a lilac flower.  The species name vulgaris translates to the more modern ‘common’.

On a lilac bush, the flowers appear in spikes.  Each spike has a central stem with the secondary (and sometimes tertiary) branches ending in flowers.  The flower clusters are called ‘thryses’ and may be up to 20 centimetres in length.  As can be seen below, the flowers bloom from bottom to top in each thryse.

The buds of the lilac plant are almost as striking as the flowers themselves.  They are roughly club-shaped, with the bulbous end being divided into four compartments.  Two buds are attached at their ends to a single terminal branch.

Most of the buds, when examined at higher magnification, appear to be dusted with tiny crystalline specks.

As a bud begins to bloom, each of its four compartments opens up to form a petal.  The interior of each petal tends to be a lighter shade of purple than the exterior.  (In very sunny weather, the colour of the flowers may fade.)

Notice that the open flower has a relatively long tube connecting it to the branch.  It is this tube that gives the plant its genus name ‘Syringa’.

Compared with many other flowers, the lilac bloom is remarkably simple in structure.  Individual flowers are from 0.5 to 1 centimetre in diameter and have four petals that are fused together where they meet the long tubular base.  As often happens in nature, mistakes in DNA replication can produce anomalies such as the flower shown below, which has five petals!

A closer look reveals four bright yellow anthers (male, pollen producing structures) packed closely together at the point where the tube widens out to form the petals.  The stigma (female, pollen accepting structure) is held by the style in a position beneath the anthers and is not visible.

Under the microscope, one of the anthers appears encrusted with pollen.

The single green stigma is divided at its tip into two parts.

Lilac pollen appear egg-shaped and have several longitudinal grooves on their surface.  Many small dimples pockmark the surface of each grain.

Phase-contrast illumination at a higher magnification resolves more of the surface detail.

Once insects have fertilized the flowers, many pale green fruit form on the branches.  At a later stage, the fruit dry out to form capsules containing two seeds each.  (Notice the characteristic heart-shaped leaves.)

My parents’ home was built on land which had been a large garden containing many lilac bushes.  During construction, the lilacs at the edge of the property were left standing.  This all happened sixty years ago, and those same plants, and their descendants were the source of the lilac flowers used in this article.  Lilacs are not only beautiful to look at, and wonderful to smell, but they are also very long-lived!



Photographic Equipment

The photographs in the article were taken with 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. The lenses screw into the 58 mm filter threads of the camera lens.  (These produce a magnification of from 0.5X to 10X 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 828.  (The magnification here is about 14X for a 4x6 inch image.) The photomicrographs were taken with a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.  


References

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 York)

• 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, Bath, UK.