![]() | Better Farming Series 02 - The Plant: the Stem; the Buds; the Leaves (FAO - INADES, 1976, 30 p.) |
![]() | ![]() | The leaves |
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Where are the leaves found?
· Leaves grow from leaf
buds.
· Leaves are found on stems and side
shoots or branches.
· They are joined to the
branches by the leaf-
stalk.
Pick up some leaves of a mango tree or coffee tree. Let us look at them.
· Leaves are usually of a green
colour, more or less dark.
· They are joined
to the stem by a stalk called the leaf- stalk.
· The leaf-stalk is continued into the leaf by the
midrib.
· Other smaller veins branch out from
the midrib. These are the primary and secondary veins.
· The whole flat part of the leaf is called the leaf
blade or lamina.
A
leaf
Some plants have a short leaf- stalk.
For example, coffee,
orange, hibiscus, guava.
Some plants have a long leaf- stalk.
For example, papaw or
papaya, sweet potato
The leaf-stalk
Some plants do not have a leaf- stalk.
The leaves of maize,
millet or rice surround the stem.
There is no leaf-
stalk.
In the middle of the leaf there is the midrib.
On each side
of the midrib other veins branch off.
These are the primary veins.
They
are smaller. These primary veins divide into many still smaller veins.
Perhaps you have seen a leaf that has been eaten by
insects.
The leaf tissue has gone and only the veins are left. It is like a
spider's web.
What are the veins for?
They carry the sap.
The sap passes along the stem
vessels.
Then it enters the vein vessels.
Cut a palm frond and you will see the sap flow. The vessels of the palm frond carry the sap.
In a man's body, the vessels carry the blood.
In a plant, the
vessels carry the sap.
Sap is the blood of plants.
The leaves of yam are not like those of cassava.
You can
recognize a plant by looking at the leaves.
Leaves are simple or compound.
· Simple leaf
The simple leaf can be entire or
lobed.
Entire simple leaf
Examples: yam , millet, okra., hibiscus,
maize, cocoa, teak, coffee
Lobed simple leaf
Examples: cassava, cotton
· Compound leaf
Look carefully at the drawing of a groundnut leaf. What it shows
is not four groundnut leaves. It is a single leaf.
But this leaf is made up
of a midrib bearing four little leaves.
These little leaves are called
leaflets.
The midrib of a compound leaf is not a stem.
So there is never a
bud between the midrib and the leaflets.
A groundnut
leaf
To live, a man feeds and breathes.
To live, a plant also
feeds and breathes.
THE PLANT FEEDS
· The plant takes up food from
the soil through its roots. It takes water and mineral salts from the soil (see
Booklet No. 1, page 17). But it has to change the water and mineral salts.
A
baby drinks only milk. Its hair grows and so do its arms and legs.
It becomes
strong and heavy.
The baby has changed the milk in its stomach into hair,
fat, muscles, etc.
· The leaf changes the water and
mineral salts taken from the soil by the roots. Water and mineral salts make up
the raw sap (see Booklet No. 1, page 19, and Booklet No. 2, page 21 ).
The
leaf changes the raw sap into elaborated sap.
The leaf sends the elaborated
sap into the buds, flowers, fruits, stem and roots.
The elaborated sap feeds the whole plant.
· The leaf changes the raw sap into elaborated sap.
The elaborated sap FEEDS:
The elaborated sap
feeds
· The leaf feeds the
plant.
It receives the raw sap; it changes the raw sap into elaborated
sap.
This change is called plant material synthesis.
What is plant material synthesis?
· Heaps of sand, wood and bricks
are not a house.
To build a house you have to put them together.
You join
them with cement.
The cement changes the wood, sand and bricks into a house.
· Water and mineral salts cannot
feed the plant.
They have to be put together, they have to be joined.
How
are water and mineral salts joined together?
· The leaves live in the
air.
The air contains carbon dioxide gas.
The carbon dioxide gas is made
of oxygen and carbon.
The leaf keeps the carbon and gives off oxygen.
· The carbon joins the mineral
sale and the water.
The mineral salts and water are changed into elaborated
sap.
The elaborated sap can then feed the plant.
The carbon changes the
raw sap into elaborated sap.
This is plant material synthesis.
To join
sand, wood and bricks with cement requires work.
You can't have a house
without men's work, men's energy.
To join water and mineral salts with carbon
also requires work and energy.
· Light gives the leaf this energy.
Light enables the leaf to change raw sap into elaborated
sap.
At night there is no light, and the raw sap is not changed.
Light enables the leaf to change
raw sap into elaborated
sap
The plant gets water and mineral salts from the soil.
This is
inorganic matter.
This inorganic matter is changed by light and carbon and
becomes elaborated sap.
The elaborated sap feeds the plant.
Just as blood
enables a man to make his muscles, hair, bones, so elaborated sap enables a
plant to make leaves, wood, fruits. The leaves, the wood, the fruits are organic
matter.
Inorganic matter has become organic matter.
To live, a man feeds and breathes.
To live, a plant also
feeds and breathes.
A plant breathes through its
leaves.
When it is hot, a man sweats, he transpires.
A plant also
transpires.
The water in the sap evaporates, the leaf gets dry.
The plant
is
thirsty.