Tree
A tree is a
tall plant with a trunk and branches made of wood. Trees can live for many years. The oldest tree ever
discovered is approximately 5,000 years old and the oldest tree from the UK is
about 1,000. The four main parts of a tree are the roots, the trunk,
the branches, and the leaves.
The roots of a tree are usually under
the ground. However, this is not always true. The roots of the mangrove tree
are often underwater. A single tree has many roots. The roots carry nutrients and water from
the ground through the trunk and branches to the leaves of the tree. They can
also breathe in air. Sometimes, roots are specialized into aerial
roots, which can also provide support, as is the
case with the banyan tree.
The trunk is the main body of the
tree. The trunk is covered with bark which
protects it from damage. Branches grow from the trunk. They spread out so that
the leaves can get more sunlight.
The leaves of a tree are green most
of the time, but they can come in many colors, shapes, and sizes. The leaves take
in sunlight and use water and food from the roots to make the tree grow and reproduce.
Trees and shrubs take
in water and carbon dioxide and give out oxygen with sunlight to form sugars. This is the opposite of what animals do in respiration.
Plants also do some respiration using oxygen the way animals do. They need
oxygen as well as carbon dioxide to live. Trees are renewable
resources because, if cut down, other trees
can grow in their place.
Growth of the trunk
As a tree grows, it may produce growth rings as new wood is laid down around the old wood. In
areas with a seasonal climate, wood produced at different times of the year may
alternate light and dark rings. In temperate climates, and tropical climates
with a single wet-dry season alternation, the growth rings are annual, each
pair of light and dark rings being one year of growth. In areas with two wet
and dry seasons each year, there may be two pairs of light and dark rings each
year; and in some (mainly semi-desert regions with irregular rainfall), there
maybe a new growth ring with each rainfall
In tropical rainforest regions, with a constant year-round climate, growth is continuous.
Growth rings are not visible and there is no change in the wood texture.
In species with annual rings,
these rings can be counted to find the age of the tree. This way, wood taken
from trees in the past can be dated, because the patterns of ring thickness are
very distinctive. This is dendrochronology.
Very few tropical trees can be accurately dated in this manner.
The roots of
a tree is almost always underground, usually in a ball-shaped region cantered
under the trunk, and extending no deeper than the tree is high. Roots can also
be above ground or deep underground. Some roots are short, some are meters long.
Roots provide support for the parts
above ground, holding the tree upright, and keeping it from falling over in the high wind.
Roots take in water,
and nutrients, from the soil. Without help from fungus for better uptake of nutrients, trees would be
small or would die. Most trees have a favorite species of fungus that they
associate with for this purpose.
Branches
Above ground, the trunk gives height
to the leaf-bearing branches, competing with other plant species for sunlight.
In all trees, the shape of the branches improves the exposure of the leaves to
sunlight. Branches start at the trunk, big and thick, and get progressively
smaller the farther they grow from the trunk. Branches themselves split into
smaller branches, sometimes very many times, until at the end they are quite
small. The small ends are called twigs.
Leaves
The leaves of a tree are held by the branches. Leaves are usually held
at the ends of the branches. The, although some have left along the branches.
The main functions of leaves are photosynthesis and
gas exchange. A leaf is often flat, so it absorbs the lightest, and thin, so
that the sunlight can get to the green parts in the cells, which convert sunlight, carbon dioxide from the atmosphere, and water from the roots, into glucose and oxygen.
Most of a tree's biomass comes
from this process.
Most leaves have stomata,
which open and close, and regulate carbon
dioxide, oxygen, and water vapor exchange
with the atmosphere.
Trees with leaves all year round
are evergreens, and those that shed their leaves are deciduous. Deciduous trees and shrubs generally lose their leaves
in autumn as it gets cold. Before
this happens, the leaves change color. The leaves will grow back in spring.
Exceptions
The word "tree" in English
means a long-lived plant having an obvious main stem, and growing to a
considerable height and size. Thus not all trees have all the organs or parts
as mentioned above. For example, most (tree-like) palms are not branched,
and tree
ferns do not produce bark. There are also more
exceptions.
Based on their general shape and
size, all of these are nonetheless generally regarded as trees. Trees can vary
a lot. A plant that is similar to a tree, but generally smaller, and may have
multiple trunks, or has branches that arise near the ground, is called a
"shrub", or a "bush". Since these are common In English words there is no precise differentiation between shrubs and trees.
Given their small size, bonsai plants
would not technically be "trees", but are true "trees".
Do not confuse the use of trees for a species of plant, with the size or shape
of individual specimens. A spruce seedling does not fit the definition of a
tree, but all spruces are trees.
Mango
Mangifera indica, commonly known as mango, is a species of flowering plant in the sumac and poison ivy family Anacardiaceae. It is native to the Indian subcontinent where it is indigenous. Hundreds of cultivated varieties have been introduced to other warm regions of the world. It is a large fruit tree, capable of growing to a height and crown width of about 30 meters (100 ft) and trunk circumference of more than 3.7 meters (12 ft). Read more...
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