Age of a tree
Trees are appreciated for their beauty, fruits and shade they
provide. They are also precious for
maintaining a suitable environment for all living creatures on earth.
Many of the big trees or giant redwoods (Sequoia species)
that grow on the Western slopes of California are famous for their big size. Some
of these trees are also very old and have been living on the earth for more
than 4000 years!
The trunk underneath the bark of every tree grows thicker as
the tree grows older. Also, the wood that grows in winter is denser and harder than
the wood that grows in summer.
Because of this, a ring-like structure is formed inside the
tree every year. These rings are of brown and cream colours which occur
alternatively in the tree trunk. The centralmost part is called the ‘pith’.
To find out the age of a tree, scientists count the number of
rings present in the trunk of the tree, which tells the exact age of a tree.
How is grafting done in
trees?
Grafting is a method of vegetative propagation by joining a
short section of the stem (scion) to another (understock) in such a way that
both grow together and continue to develop as a single plant.
The most important use of grafting is that it makes it
possible that the young trees or shrubs will produce the same quality of flower
or fruit as that of the parent tree. A twig taken from a tree and grafted into
another tree will produce the same type of fruit borne by the tree from which
it was taken.
Different methods can be followed by different people for
inserting the buds or scions into the stock of the other plant. But two
important rules must be observed.
Firstly the genetic compatibility of scion and stock must be
kept in mind that is, only related species of trees or shrubs should be
combined. For example, apples can be grafted on pears, and peaches can be grafted
on apricots, plum or other stone fruit trees. But apples cannot be grafted on
peach trees.
Secondly, care must be taken that the cambium layer which
carries the vital sap of the scion is in touch with the cambium layer of the
stock used for grafting.
Scientists have done lots of experiments in this field to
produce new and better varieties of fruits and flowers. Repair grafting is also
done to help injured or infected plants.
Century
plant
According to a common belief a century plant blooms only when
it reaches the age of a hundred years. This was the reason for naming it a
century plant. But the belief is not true although the name remains popular.
The time of blooming depends on individual plants and can be
quite different for each. The climate also plays an important role. In very warm
places flowers can bloom within twenty years. In colder climates, it may take
sixty years or more.
The technical name for the century plant is ‘agave’. The
plant has a large “rosette” of thick fleshy leaves ending in a Tharp point. The
stem from which leaves rise is usually very short and it looks as if the leaves
are coming straight from the roots or the earth.
A tall stem or “most” grows from the center of these leaves
when the plant is ready for flowering. Many small flowers appear on this mast.
The flowering seems to require a lot of nourishment from the plant because
after this the plant usually dies.
The stalk of the plant grows quite fast, and when the growth
starts, there is a rush of sap to the base of the stalk. People in Mexico make
use of this sap to prepare a tasty drink called “pulque” which is the national
drink of Mexico.
The large bud is removed as soon as it is ready to emerge and
a cavity is scooped in the centre of the plant. A large quantity of the sweet
sap from the leaves collects into it which is collected in pigskin bottles and
then allowed to ferment in a repository. The thick and milky drink thus
obtained is said to be a very nourishing drink by the Mexicans.
What are fossils?
The remains and traces of plants and animals that inhabited the earth in the past help scientists find and know about them. These remains are called fossils, most of which are found preserved in rocks.
Some of the fossils are millions of years old. Sometimes they
are the bones, shells, scales or other hard parts of animals. Even fossil rain
imprints, ripple marks and fossil fuels are useful in scientific studies.
The study of fossils was not seriously done until the late
seventeenth century. When a French naturalist found the bones of elephants,
hippopotamus, and some other animals in the rocks near Paris, it was discovered
that the climate of that area must have been much warmer and different in
earlier times. Charles Darwin made use of fossils to show how living forms developed
from very early times to the present.
Why are fertilizers important?
When soil is used for growing vegetables etc., they take away some important ingredients of the soil and the fertility of the soil is greatly reduced. To make the soil fertile and rich so that the crops on it grow rich and healthy, a few things are added by man to it, and we call them fertilizers.
Manures of different kinds were used by farmers even in
ancient times. Wastes such as decaying plants, leaves, and animal wastes, all can
be made useful in the form of manures to improve the quality of food we grow in
the form of plants.
Today, chemical fertilizers have become very popular and are of great help to farmers.