The vascular cambium is a lateral meristem that increases the diameter of stems and roots through secondary growth. It is composed of fusiform initials that divide to form vertical tissues and ray initials that form horizontal tissues. In dicots, intrafascicular cambium initially develops within vascular bundles and interfascicular cambium develops between bundles, eventually joining to form a complete cambial ring. The cambium divides to produce secondary xylem internally and secondary phloem externally. Its seasonal activity varies the structure of the tissues produced.

2. VASCULAR CAMBIUM
• Introduction
# In majority of monocotyledons and pteridophytes the primary plant body
structurally and functionally complete. In most dicotyledons and
gymnosperms,primary growth is soon followed by secondary growth.
# Secondary growth take place by the activity of cambium
# The vascular cambium Is a lateral meristem. It is a continuous sheath of the
meristematics cells. The vascular cambium increase the diameter or girth of plant by
secondary growth .
#Cambium divide and produce the new cells toward the inner as well as outer side.
# In dicot stem the first procambium that develops from promeristem present in the
form of patches in each vascular bundle between the primary phloem and primary
xylem called intrafascicular cambium or fascicular cambium.
# The new cambium develop from the interfascicular region, some parenchymatous
cells become meristematic and forme the secondary cambium which present
between the two vascular bundles called interfascicular cambium .
# The fascicular and interfascicular cambium joined together and form a complete
ring of cambium cells known as cambial ring.

4. Structure of cambium
• The vascular cambium is made up of the two components-
1-Fusiform initial and 2- Ray initial
1- Fusiform initial- These cells are spindle shaped and long with
their pointed ends. It divide to form all cells of vertical system. The
arrangement of the fusiforn initial is mainly two types in different
plants. 1- stratified arrangements and 2-non stratified
arrangement.
# Stratified arrangement:When the fusiform initial cells arrange
horizontally in the same level , it is called stratified arrangement. Eg.
Dalbergia sisso. and the cambium is called stratified cambium.
# Non stratified arrangement: When the fusiform initial are not
arranged regularly in horizontally row it is called Non stratified
arrangement,and the cambium is called non stratified cambium.

5. 2. Ray initial –The ray initial cells are Smaller than the fusiform initial
with their flattened axis.The ray initials are isodiametric cells—about
equal in all dimensions—and they produce the vascular rays, which
constitute the horizontal system of secondary tissues; this horizontal
system acts in the translocation and storage of food and water.

7. Function of cambium
• The main function of cambium is the increasing the girth of the plant
i.e. The secondary growth of the complex permanent tissues (xylem
and phloem) the cambium divide tangential division and add new cells
toward both side. The cambium forms the cells outside differentiate
into secondary phloem and which produce toward inner side are
differentiate into secondary xylem. The ray initial gives rise to xylem
and phloem rays.
• During the division of cambium it gives an appearance of
multilayered cambium known as cambial zone, but actually the
cambium remain single layered.

9. Seasonal activity of cambium
• Cambium of some plants remain active for their entire life time i.e cambial
cell divides and resulting cells mature to form xylem and phloem element.
• Not the all plant show the cambial activity. The seasonal activity usually
found in the plants of the tropical region.
• In autmn season cambium enters in dormant state and last for the end of
summer. In spring season cambium again become active.
• In autmn season (unfavorable) cambium is less active and produce the
thick walled narrow, dark brown and much smaller xylem tissue(vessels are
narrow)
• In spring season (favorable) cambium become more active and produse
large size, thin walled and light color xylem element (vessels are large)
which conduct more water than those produce in unfavorable conditions.

11. Multiple choice questions
• Q:1 In dicot stem the cells of horizontal system produced from-
• (a) fusiform initial (b) cork cambium
• (c) Fascicular cambium (d) ray initial
• Q:2 Vascular cambium is-
• (a) apical meristem (b) lateral meristem
• (c) intercalary meristem (d) none of these
• Q:3 Intra-fascicular cambium present in-
• (a) between the xylem and phloem (b) between the two different vascular bundles
• (c) outside the xylem (d) in cortex
• Q:4 Which type of vascular tissue produced just outside the vascular cambium-
• (a) xylem (b) phloem
• (c) heartwood (d) parenchyma
• Q:5 Xylem tissue is responsible to transporting of what substance?
• (a) starch (b) sugar molecules
• (c) water and minerals (d) chlorophyll

12. • Ans:1 - (d) ray initial
• Ans:2 - (b) lateral meristem
• Ans:3 - (a) between xylem and phloem
• Ans:4 - (b) phloem
• Ans:5 - (c) water and nutrients

13. • Q:6 If four radial vascular bundle are present the structure will be-
• (a) monocot stem (b) monocot root
• (c) dicot root (d) dicot stem
• Q:7 Fascicular cambium present in dicot stem is-
• (a) Intercalary meristem (b) primary meristem
• (c) secondary meristem (d) apical meristem
• Q:8 Which one of the tissue formed in stems from cells cut off by the cambium on its inner side-
• (a) bast fibres (b) wood fibres
• (c) phalloderm (d) sieve tubes
• Q:9 Vascular cambium and cork cambium are-
• (a) part of secondary xylem and secondary phloem (b) part of epidermis
• (c) lateral meristem (d) intercalary meristem
• Q:10 In dicot stem the secondary growth take place by-
• (a) primary cambium (b) secondary cambium
• (c) development of cambium in stele region (d) development of cambium in stele and in
• cortical region

14. • Ans :6 -(d) dicot root
• Ans :7 -(b) primary meristem
• Ans :8 -(b) wood fibres
• Ans :9 -(c) lateral meristem
• Ans :10 -(d) development of cambium in stele and cortical region