When Joyce Kilmer wrote (1913) "I think that I shall never see, a poem lovely as a tree" he may have been dreaming of one of the 300 native tree species of North America or one of thousands of varieties used as ornamentals and as providers of food, shade, building supplies, and soil stability in forests, fields, lawns, and gardens around the world.

The wise author of the ancient Chinese proverb, "One generation plants the trees under which another takes its ease," points at the large difference in life history strategy between humans and most tree species. Trees such as California's majestic coastal redwoods or the South's moss-draped live oaks sporting life spans of 3,300 and 300 years, respectively, easily outlive their human admirers. However, very few living things on Earth can rival the ancient, dwarfed and knarled bristle cone pines surviving at timberline in California, Nevada, and Utah for up to 4,700 years. Each of these wooden sentries shelters climatic data captured in its annual rings of growth that correlate with important events like Columbus' discovery of North America or Mt. Vesuvius' ash entombing of ancient Pompeii. In fact, many standing dead pines date back to 7,000 BC.

Trees are woody plants that often continue growing until their death. As perennials with a distinct, self-supporting main stem (trunk) that contains woody tissues, trees produce secondary limbs and branches. Although some trees only grow to four meters high, the tallest species, such as the mighty redwoods and eucalyptus, reach heights greater than 110 meters. The largest tree in North America, the General Sherman giant sequoia in California's Sequoia National Park, has reached 84 meters and a diameter of 11 meters...and is still growing at an amazing rate sufficient to annually provide enough new timber to construct a six-room house.

The root systems of these massive trees reach out for nutrients and water, but also anchor the trees in the soil. Some of the larger sequoias (weighing more than 12 million pounds, equivalent to a small ocean-going freighter) extend their area of influence throughout four square acres of forestland. The fine, fibrous ends of the roots not only hold the soils in place, thereby preventing erosion, but also provide a micro-ecosystem, the rhizosphere, for synergistic bacteria to help the trees process nitrogen, phosphorus, and other vital nutrients and minerals.

In this gallery, you will find just a slice of the tree diversity for both study and aesthetic appreciation, with our microscopes providing a close-up view of stained thin sections, which reveal the minute structural details of selected tree tissues. Each entry contains a cross, radial, and tangential section of stained wood accompanied by an abstract of information about the particular tree.

Glossary of Terms - The wide variety of technical terms utilized in describing the microscopic anatomy of tree thin sections is complex. This section contains a brief review of the most common terms encountered by visitors in the Molecular Expressions Tree Collection pages.

American Basswood - This tree is called the "Bee Tree" because of its fundamental importance to the production of a honey. Basswoods are found throughout the eastern half of North America ranging from the northern Canadian Provinces all the way south to Florida. Many of the species can interbreed, and it is very easy to locate natural hybrids of this tree.

American Beech - Beeches can grow to heights of 110 feet and have a dense, spreading, oval crown. Propagation occurs either by seed or by rooted suckers that the tree naturally releases. Legends, both fanciful and true, have often been inscribed in the smooth bark of the beech tree. American adventurer Daniel Boone carved this short message in a Tennessee beech: "D. Boone Cilled A Bar On Tree In Year 1760."

American Chestnut - In the early twentieth century a fungal disease attacked and killed most chestnut trees. This disease probably originated in eastern Asia and was accidentally introduced into the United States. New species of American chestnut have been developed that are resistant to the fungus and this tree is now making a comeback.

American Elm - This native tree is another important species that has fallen victim to the fungal blight called Dutch Elm Disease, which was first discovered in 1930 and has since killed hundreds of thousands of trees. Efforts are being made to develop disease-resistant strains of the elm tree, but like all tree research, this will probably take many years.

American Sycamore - This native hardwood tree is a long-lived specimen with lifetimes often exceeding 500 years, although many trees become hollow after 200-300 years. The species propagates by cuttings (very easily) and naturally, by seed. Optimal growth conditions are cool, deep alluvial soils, and the tree will not adapt to acidic or marshy soils.

Balsam Fir - The fir is a creamy-white to pale brown softwood tree found primarily in Canada and in the United States from the coast of Maine to the mountains of Virginia and West Virginia. Young trees and their branches contain blisters filled with a yellowish oleoresin (commonly termed Canada balsam), which was formerly used in cementing lens elements together and mounting specimens for observation with a microscope.

Balsam Poplar - An ointment, called Balm of Gilead, was once made from the winter buds of the balsam poplar tree and was widely used to relieve congestion. The buds contain a waxy resin with disinfectant properties and this resin is still used in many modern (now termed "organic") natural health ointments. Bees collect the resin and use it to seal the hive from intruders, such as mice and other insects, which might have detrimental effects on the hive.

Bitternut Hickory - Bitternut hickory nuts are encased in a husk that blackens when they ripen in September or early fall. The bitternut is the largest of the hickories, and is the only hickory tree that produces a nut that is not edible (or desirable) for humans because of its extreme bitterness. Because hickory wood is unsurpassed in its inherent qualities of hardness, strength, toughness, and resiliency, bitternut hickory wood is often used for tool handles--especially for impact tools such as hammers, axes, picks, and sledges.

Black Cherry - Black cherry is a member of the Rose family of deciduous and broadleaf evergreen shrubs and trees that inhabit nearly the entire North Temperate Zone, with a few reaching to the Andes. The Prunus genus comprises over 400 species and includes all of the plums, cherries, apricots, peaches, and almonds in addition to the Japanese flowering cherries and similar shrubs.

Black Locust - This beautiful tree is planted widely around the world as an ornamental tree because of its fragrant, attractive flowers and beautiful foliage. The tree grows very rapidly (sometimes becoming a pest) to heights of over 80 feet, often with a bifurcated trunk and having a scaly, furrowed bark that becomes gray-brown upon maturation.

Black Tupelo - A hardwood tree that shines during the Indian summer. Members of the tupelo family often attain a height of 80 to 85 feet and occasionally taller in the wild, and features horizontally oriented branches that droop gradually at the ends. The leaves range from three to five inches long and are broad with a pointed tip, but lack marginal teeth.

Black Walnut - The roots of the black walnut produce a substance known as juglone (5-hydroxy-alpha-napthaquinone). This biochemical is toxic to many plants such as the tomato, potato, black and blue berries, and other plants that may grow within a 50 to 60 foot radius of the trunk. Not all plants are sensitive to juglone and many trees, vines, shrubs, and flowers will thrive in close proximity to a black walnut tree.

Black Willow - A beautiful broadleaf hardwood that naturally lines the banks of rivers and streams. Black willow trees are well known for their ability to assist in preventing erosion, and often naturally keep many river and creek banks from washing away.

Butternut - Unfortunately, this tree is being killed throughout its growth range by Sirococcus claviginenti-juglandacearum, a fungus most likely introduced from outside of North America. More than 90 percent of all butternut trees in Ontario and western Quebec are now infected with the deadly canker. This disease has led to the butternut tree being placed on the endangered plant listing in the United States.

Douglas Fir - One of the largest trees in the world, the Douglas fir is named for David Douglas, a famous botanist who introduced the seeds into Europe. This tree is among the biggest trees in the world and it is particularly abundant in Oregon and Washington where it forms great forests. A specimen in Oregon is thought to contain enough wood to build six homes.

Eastern Cottonwood - According to the Indian legend, the original design for a teepee was discovered by a brave who twisted a cottonwood leaf around his fingers, forming a miniature teepee. Pulp from this wood is often used to make high-grade book and magazine paper.

Eastern Hemlock - Needles from this softwood conifer was used to make a tea that is the basis for old-fashioned root beer. The tree often reaches heights of 100-plus feet and the trunk is branched down to the base in mature specimens. Cones are egg-shaped and rather small, averaging three quarters of an inch in length.

Eastern Red Cedar - This softwood was once known as "The Tree of Life" to many Indian tribes, because they were able to use practically every piece of the tree. Another name for the tree, pencil cedar, is derived from the extensive use of this wood to make pencil slats. At one time this was the most important use for cedar but today, because of the scarcity of suitable material, the wood is used in less than 10 percent of the pencils produced in the United States.

Northern Red Oak - A broadleaf hardwood that produces acorns used as a dietary staple by American Indians. The shiny green leaves, which are oblong and up to nine inches long with bristle-tipped lobes, often turn deep to bright red in the fall. The red oak is one of the easiest trees to transplant and is a useful shade tree, except in regions affected by the oak wilt disease.

Northern White Cedar - Cedar contains natural preservatives that make it one of the most decay-resistant and insect-tolerant woods available. This particular wood is very popular with craftsmen, because it can be easily worked by hand or with power tools.

Pecan - Pecan trees are propagated by seed and require a very deep, fertile, and the moist soil typically found in the south. Pecan is one of the most important cultivated nuts of North America, grown primarily in Georgia and Texas, but also in most southern states and California. Pecan trees do not start producing pecans until they are 4 to 5 years old.

Post Oak - The woods of various oak species belonging to the post and white oak group (Leucobalanus) cannot be distinguished with any great degree of certainty. Post oak wood is widely used for flooring, farm (non-motor) vehicles, mill products (sash, doors, trim, wainscoting, general millwork), furniture (especially desks and tables, chairs, frames for upholstered furniture), kitchen cabinets, fixtures, railroad cars, boxes, crates, and pallets.

Quaking Aspen - An unusual male aspen tree, located in the Wasatch Mountains of Utah, has actually been named Pando and weighs about six million kilograms, or 13 million pounds. Several scientists have speculated that the quaking aspen Pando is the heaviest living "being" on the planet.

Red Pine - Like the white pine, red pine was often used in ship masts in both large and small sailing vessels. In fact, the British Navy was buying large red pine tree trunks from North America as late as 1875.

Redwood - The Coastal Redwood and the Giant Sequoia tree are named after the Cherokee Indian Sequoyah, honoring this distinguished chief who conjured an alphabet for his people and whose statue stands in the rotunda of the United States Capitol. The redwood is one of the world's tallest trees (if not the tallest) and some specimens have been measured at lengths of 350 feet.

Rock Elm - The rock elm has the hardest and heaviest wood of all the elms, including the European versions. The devastation of most American elm trees due to the Dutch elm disease has rendered the species much too rare for commercial use.

Silver Maple - An ornamental hardwood that causes problems with falling limbs during severe weather. The silver maple tree grows to heights of 80 to 100 feet and has a smooth light bark with foliage that turns red in the fall. Propagation is by seed, and the silver maple prefers cool, moist soil with a high water table.

Sitka Spruce - Sitka spruce has the highest timber yields due to the rapid growth of its canopy, and that contributes to the tree's high commercial value. Spruce trees are famous for their majestic appearance as huge needle-leaf evergreens of tremendous horticultural significance. These trees are widely utilized in the timber industry and are an important ingredient in paper pulp.

Slippery Elm - In times of famine, early American settlers used the slippery elm as a survival food. It is rumored that George Washington and his troops survived for several days on slippery elm gruel during the bitter winter at Valley Forge.

Sugar Maple - Like many other species in the Aceraceae family, the sugar maple is a tall tree and many specimens reach a height of almost 100 feet. Sugar maple is a very slow-growing tree (much slower than many other hardwoods), but it is an outstanding ornamental and sparkles in the fall with a dazzling display of color and hue. Sugar maple and black maple wood is often sold indiscriminately as hard maple, which can be distinguished from the soft maples through examination of the rays.

Sugar Pine - Today, the biggest sugar pine measures 270 feet high with a trunk circumference of 348 inches and a branch spread of 68 feet on all sides. This huge specimen was recorded by the National Register of Big Trees in 1992 and can be visited at the Yosemite National Park, in California.

Sweetgum - The history of this tree dates back 55 million years to a time when Greenland had a sub-tropical climate. Sweetgum is the only commonly cultivated species of the Liquidambar genus, which is named after the fragrant resin of an Asiatic species. In the fall, sweetgums display a dazzling array of yellow, red, and purple colors on their lobed, maple-like leaves.

Tamarack - Tamarack is a member of the Pinaceae pine family, and around 10 species of these deciduous trees have been cataloged. All larches are valuable timber trees and are widely grown as ornamentals for their attractive foliage and shape. The roots of the Tamarack were used to secure deck timbers in ancient sailing vessels.

Western Hemlock - A member of the pine family (Pinaceae), hemlocks are beautiful evergreen trees that have about 10 individual species. These trees are excellent screen and background plants and have a delicate foliage with numerous fan-like leafs.

Western Red Cedar - Millions of homes have been built with western red cedar, because this wood is very lightweight and easy to finish. Western red cedar is also a natural insulator. The wood is used for all purposes where durability and ease of working are of primary importance.

White Ash - The Ash (Oleceae or olive) family is a group of 65 species, most of which are deciduous trees of the North Temperate Zone, and serve as ornamental and timber trees. Ash trees grow very quickly in general and have strong wood, thus they endure storms far better than many rapid-growing species. In general, the foliage and fall color display is attractive, but varies from species to species.

White Oak - The U.S.S. Constitution, made with the wood of the white oak, was called "Old Ironsides" because cannonballs were rumored to bounce off the ship's strong wood siding. Oaks are generally considered some of the finest hardwood timber trees and the cadre of over 450 species also includes ornamentals that decorate lawns, parks, and streets.

White Pine - White pines, one of the most utilized timber pines in North America and perhaps the most beautiful of all eastern species, often grow to heights of 140 feet with trunk diameters ranging between 3 and 5 feet. The lumber was first exported to England in 1605, and it soon became fully appreciated by the British royalty whose American colonial subjects "marked" trees for exclusive use by the Royal Navy for ship construction.

Yellow Birch - A majority of the evergreen birch (Betulaceae) family are medium-tall deciduous trees that are more often grown for timber or aromatic properties than as an ornamental. The Betula genus has between 50 and 60 species, mostly from North America or Asia. The yellow birch is an ancient species that dates back to the Ice Age and although the tree is found as far south as the Carolinas, it thrives in cold northern climates.

Yellow Buckeye - The buckeye is a member of the Hippocastanaceae family of trees, which contains approximately 15 species of deciduous trees falling into two categories: the horsechestnuts and buckeyes. General William Henry Harrison made the Buckeye tree famous during his presidential campaign in 1840 when he drew attention to Ohio's Buckeye wood cabins and walking sticks.

Yellow Pine - Leaves are needle-like and borne in sheathed clusters of three, growing 6 to 9 inches long on the yellow pine. The cones range 3 to 5 inches in length and have long scales with very sharp points. Although the yellow is not the most beautiful of pine trees, it is tolerant of a wide range of soil conditions, and is seldom seriously affected by insects or diseases. Yellow pines are rapidly growing when young, and can reach a height of 90 feet at maturity.

Yellow Poplar - The tulip tree is well named, having flowers that rival earth-bound tulips. The blossoms, ranging from a greenish yellow to a deep orange, appear on the tree in May and June. Southern housewives traditionally pick up dropped Yellow (or Tulip) Poplar blossoms and float them in shallow dish of water to provide an interesting table piece.

1. P. Lanzara and P. Mariella, "Simon & Schuster's Guide To Trees", Simon and Schuster, New York, 300 pages (1977).

2. P. Chandler, D. Cook, G. DeWolf Jr., G. Jones, K. Widin, "Taylor's Guide To Trees", Houghton Mifflin Co., New York, 480 pages (1961).

3. A. Panshin, C. Zeeuw, "Textbook Of Wood Technology", McGraw-Hill, New York, Fourth Edition, 722 pages (1949).

4. F. Jane, "The Structure Of Wood", A. and C. Black, Niell and Company, Ltd., Edinburgh, Second Edition, 478 pages (1956).

5. C. Mattheck and H. Kubler, "Wood-The Internal Optimization of Trees", Springer-Verlag, New York, 129 pages (1995).

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Photomicrography and text by Laurence D. Zuckerman, Omar Alvarado, and Michael W. Davidson.

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