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tree, perennial woody plant with a single main stem (the trunk, or bole) from which branches and twigs extend to form a characteristic crown of foliage. In general, a tree differs from a shrub in that it has a single trunk, it reaches a greater height at maturity, it branches at a greater distance from the ground, and it increases in size by producing new branches and expanding in girth while a shrub often produces new shoots from ground level. Trees fall into three major divisions: angiosperms, gymnosperms, and pteridophytes. Angiosperms are the most common type, where seeds carried in various fruits are the agents of reproduction. Trees and shrubs may be deciduous, with broad leaves that are shed at the end of the growing season, or evergreen (see conifer), with needlelike or scalelike leaves that are shed at intervals of between 2 and 10 years, thus maintaining green foliage at all seasons. Trees are identified both by the characteristic color and shape of the leaf and by their overall appearance, e.g., the degree and angle of branching, the shape of the crown, and the texture of the bark. Their age can be determined from a count of the annual rings, which represent the diameter growth of a tree each year. Besides their enormous importance in providing oxygen and moisture for the atmosphere and removing harmful carbon dioxide, trees are an important source of food, of wood, and of numerous products (e.g., resins, rubber, quinine, turpentine, and cellulose for the manufacture of paper and various synthetic materials) derived from their wood, bark, leaves, and fruits.


See H. Johnson, The International Book of Trees (1973) and The World of Trees (2010); L. Line and A. Sutton, Audubon Society Book of Trees (1981); A. C. Barefoot and F. W. Hankins, Identification of Modern Tertiary Woods (1982); F. Stafford, The Long, Long Life of Trees (2016).

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A perennial woody plant at least 20 ft (6 m) in height at maturity, having an erect stem or trunk and a well-defined crown or leaf canopy. However, no sharp lines can be drawn between trees, shrubs, and lianas (woody vines). The essence of the tree form is relatively large size, long life, and a slow approach to reproductive maturity. The difficulty of transporting water, nutrients, and storage products over long distances and high into the air against the force of gravity is a common problem of large treelike plants and one that is not shared by shrubs or herbs.


Almost all existing trees belong to the seed plants (Spermatophyta). An exception are the giant tree ferns which were more prominent in the forests of the Devonian Period and today exist only in the moist tropical regions. The Spermatophyta are divided into the Pinophyta (gymnosperms) and the flowering plants, Magnoliophyta (angiosperms). The gymnosperms bear their seed naked on modified leaves, called scales, which are usually clustered into structures called cones—for example, pine cones. By contrast the seed of angiosperms is enclosed in a ripened ovary, the fruit. See Magnoliophyta, Pinophyta

The orders Cycadales, Ginkgoales, and Pinales of the Pinophyta contain trees. Ginkgo biloba, the ancient maidenhair tree, is the single present-day member of the Ginkgoales. The Cycadales, characteristic of dry tropical areas, contain many species which are small trees. The Pinales, found throughout the world, supply much of the wood, paper, and building products of commerce. They populate at least one-third of all existing forest and include the pines (Pinus), hemlocks (Tsuga), cedars (Cedrus), spruces (Picea), firs (Abies), cypress (Cupressus), larches (Larix), Douglas-fir (Pseudotsuga), sequoia (Sequoia), and other important genera. The Pinales are known in the lumber trade as softwoods and are popularly thought of as evergreens, although some (for example, larch and bald cypress) shed their leaves in the winter.

In contrast to the major orders of gymnosperms which contain only trees, many angiosperm families are herbaceous and include trees only as an exception. Only a few are exclusively arborescent. The major classes of the angiosperms are the Liliopsida (monocotyledons) and the Magnoliopsida (dicotyledons). The angiosperm trees, commonly thought of as broad-leaved and known as hardwoods in the lumber market, are dicotyledons. Examples of important genera are the oaks (Quercus), elms (Ulmus), maples (Acer), and poplars (Populus).

The Liliopsida contain few tree species, and these are never used for wood products, except in the round as posts. Examples of monocotyledonous families are the palms (Palmae), yucca (Liliaceae), bamboos (Bambusoideae), and bananas (Musaceae).


The morphology of a tree is similar to that of other higher plants. Its major organs are the stem, or trunk and branches; the leaves; the roots; and the reproductive structures. Almost the entire bulk of a tree is nonliving. Of the trunk, branches, and roots, only the tips and a thin layer of cells just under the bark are alive. Growth occurs only in these meristematic tissues. Meristematic cells are undifferentiated and capable of repeated division. See Flower, Lateral meristem, Leaf, Root (botany), Stem


Height is a result of growth only in apical meristems at the very tips of the twigs. A nail driven into a tree will always remain at the same height, and a branch which originates from a bud at a given height will never rise higher. The crown of a tree ascends as a tree ages only by the production of new branches at the top and by the death and abscission of lower, older branches as they become progressively more shaded. New growing points originate from the division of the apical meristem and appear as buds in the axils of leaves. See Apical meristem, Bud, Plant growth

In the gymnosperms and the dicotyledonous angiosperms, growth in diameter occurs by division in only a single microscopic layer, three or four cells wide, which completely encircles and sheaths the tree. This lateral meristem is the cambium. It divides to produce xylem cells (wood) on the inside toward the core of the tree and phloem cells on the outside toward the bark. In trees of the temperate regions the growth of each year is seen in cross section as a ring. See Phloem, Xylem

Xylem elements become rigid through the thickening and modification of their cell wall material. The tubelike xylem cells transport water and nutrients from the root through the stem to the leaves. In time the xylem toward the center of the trunk becomes impregnated with various mineral and metabolic products, and it is no longer capable of conduction. This nonfunctional xylem is called heartwood and is recognizable in some stems by its dark color. The light-colored, functional outer layer of the xylem is the sapwood. See Wood anatomy

The phloem tissue transports dissolved carbohydrates and other metabolic products manufactured by the leaves throughout the stem and the roots. Most of the phloem cells are thin-walled and are eventually crushed between the bark and the cambium by the pressures generated in growth. The outer bark is dead and inelastic but the inner bark contains patches of cork cambium which produce new bark. As a tree increases in circumference, the old outer bark splits and fissures develop, resulting in the rough appearance characteristic of the trunks of most large trees.

In the monocotyledons the lateral cambium does not encircle a central core, and the vascular or conducting tissue is organized in bundles scattered throughout the stem. The trunk is not wood as generally conceived although it does in fact have secondary xylem. See Forest and forestry, Plant physiology, Plant taxonomy

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a long-lived plant (usually not under 2 m in height) with perennial woody stems and roots. In trees, as distinguished from shrubs, the main stem—the trunk with its branches forming a crown—is always well defined. Almost all trees belong to one of two groups—conifers (of the gymnosperms) or dicotyledons (of the angiosperms). The trunk and branches of a tree consist of wood and bark. The type of branching in various species is distinctive and determines their appearance. In trees grown in plantings the trunk is tall and almost cylindrical, and the crown is small and high. Trees grown in open places have short, thick trunks that widen toward the base (tapering), and their crowns begin low. As a rule, the lumber of the former is considerably more valuable. Among the monocotyledons there are trees with trunks that are thin and hollow (bamboo), poorly branched (dracena), or unbranched but bearing large leaves in place of branches (palms).

The tallest trees are the sequoia, the Douglas fir, and the eucalyptus (up to 100-110 m); the thickest are the baobabs (up to 9 m in diameter); and the longest lived are the sequoia, baobab, and dragon tree, which may live to an age of 3,000-5,000 years.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

What does it mean when you dream about trees?

The sobriquet “tree of knowledge” and the proverb “they shall be known by their fruits” reflect the ancient heritage of this archetypal dream symbol. The size and the condition of the tree may indicate how one views one’s inner strength and “growth” in the world.

The Dream Encyclopedia, Second Edition © 2009 Visible Ink Press®. All rights reserved.


A perennial woody plant at least 20 feet (6 meters) in height at maturity, having an erect stem or trunk and a well-developed crown or leaf canopy.
(computer science)
A data structure in which each element may be logically followed by two or more other elements, there is one element with no predecessor, every other element has a unique predecessor, and there are no circular lists.
A set of connected circuit branches that includes no meshes; responds uniquely to each of the possible combinations of a number of simultaneous inputs. Also known as decoder.
A connected graph contained in a given connected graph having all the vertices of the original but without any closed circuit.
A projecting treelike aggregate of crystals formed at areas of high local current density in electroplating.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. any large woody perennial plant with a distinct trunk giving rise to branches or leaves at some distance from the ground
2. any plant that resembles this but has a trunk not made of wood, such as a palm tree
4. Chem a treelike crystal growth; dendrite
5. Archaic the cross on which Christ was crucified


Sir Herbert Beerbohm. 1853--1917, English actor and theatre manager; half-brother of Sir Max Beerbohm. He was noted for his lavish productions of Shakespeare
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


(mathematics, data)
A directed acyclic graph; i.e. a graph wherein there is only one route between any pair of nodes, and there is a notion of "toward top of the tree" (i.e. the root node), and its opposite direction, toward the leaves. A tree with n nodes has n-1 edges.

Although maybe not part of the widest definition of a tree, a common constraint is that no node can have more than one parent. Moreover, for some applications, it is necessary to consider a node's daughter nodes to be an ordered list, instead of merely a set.

As a data structure in computer programs, trees are used in everything from B-trees in databases and file systems, to game trees in game theory, to syntax trees in a human or computer languages.
This article is provided by FOLDOC - Free Online Dictionary of Computing (


(1) See forests and trees.

(2) An external DOS/Windows command that displays a subfolder tree, as follows:
tree     display hierarchy

   tree /f  display files and subfolders

(3) A hierarchical structure that is conceptualized as an upside-down tree with the starting point at the top, which is the root. For example, in a company organization chart, the highest level is the executive office. The various divisions are the branches, and the departments are branches off the divisions.

The Folder Tree
The term often refers to the file/folder hierarchy on a hard disk. In Windows and Mac, the Explorer and Finder utilities are used to display these hierarchies respectively. See root.

Windows and Mac Trees
Folder hierarchies are displayed from left to right. The highest folder in the Windows example (top) is Program Files, while the highest level in the Mac (bottom) is the Utilities folder.

Windows and Mac Trees
Folder hierarchies are displayed from left to right. The highest folder in the Windows example (top) is Program Files, while the highest level in the Mac (bottom) is the Utilities folder.
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.


The tree in your dream is you. The health, size, and overall quality of the tree is indicative of how you feel about yourself. This interpretation is to be made only when the tree is the focal point of the dream. Also, consider whether the tree is alive with leaves, flowers, or fruit, or if it’s barren. You may see trees in your dream as a part of a landscape or as a secondary symbol. At those times, consider all of the details, as they may have different interpretations than the one just given.
Bedside Dream Dictionary by Silvana Amar Copyright © 2007 by Skyhorse Publishing, Inc.