Parts of the tree
Grade 8
Cross section of the tree trunk
Parts of the tree
The tree trunk consist of eight parts .They are:
• Sapwood
• Heartwood
• Cambium
• Pith
• Annual rings
• Medullary Ray
• Bark
• Inner Bark
Label diagram
1. Sapwood
• Sapwood is the outer part of the tree
responsible for receiving the water and
minerals from the roots and conducting them
around the tree to the leaves as well as for
food storage. It is located between the
heartwood and the cambium.
Location of the sapwood
2. Heartwood
• Heartwood is the non-active part of the treeusually darker in colour than sapwood- and
provides the tree with the rigidity often
necessary to support the crown. The most
durable wood for timber is from this part of
the tree. It is located between the pith and the
sapwood.
Location of the heartwood
3. Medullary Rays
• A ray consist of a strip of wood cells that allow
sap to move transversely through the wood
and provide for storage of surplus food and its
movement when required . They may appear
to radiate from the pith to the inner bark
,hence the name medullary ray is often used.
Location of the medullary rays
4. Inner bark / bast
• The inner bark distributes the food substances
provided by the leaves through the whole of
the tree. After one growing season it will
become inactive as a mean of conducting food
; it takes on a new role as the outer bark. It is
located between the cambium and the outer
bark.
Location of the inner bark / bast
5. Bark
• The bark makes up the outer sheath of the
whole tree. It serves to protect the inner parts
of the tree from:
• Fungal attack , Mechanical abrasion by
animals and other agents , Extreme
temperatures and Insect attack.
Location of the bark
6. Pith
• The pith is the center of the tree. The pith is
the result of the tree’s earliest growth –a
sapling –wood immediately surrounding it is
called ‘juvenile wood’, which is not very
desirable as timber.
Location of the pith
7. Cambium
• Cambium is the sleeves of cells located
between the sapwood and the inner bark
which covers the whole of the tree-that is its
trunk, branches and twigs. These cells are
responsible for growth of the tree both its
girth[distance around the trunk] and height.
As the cells formed during the growing season
they become sub-divided in such a way that
new cells are added to both the sapwood and
the inner bark.
Location of the cambium
8. Annual rings
• This implies that the rings of wood cells ,which
appear as bands ,are reproduced each year
and by counting the number of rings we know
how old the tree was when it was cut down.
Location of the Annual Rings
classwork
• 1. Label the cross section of the tree trunk
classwork
• 2. Give function of each part identified