Question

In a dicot root vascular cambium is
A. Partially primary and partially secondary in origin.
B. Completely primary in origin
C. Completely secondary in origin
D. Not found

Answer 1

Hint: The growth of roots and stems in girth with the help of lateral meristems is called secondary growth .Vascular cambium and cork cambium are the meristems that participate in secondary growth of dicots.

Complete answer:
Meristems: Meristems can be defined as active mitotic centres, limited to certain parts of higher plants, where cells of the meristem divide endlessly in multiple mitoses, while new cells are constantly added to the developing organ of the plant.
On the basis of development and origin meristems are of three types
1.Promeristems
2.Primary meristems
3.Secondary meristems
Promeristems: It is a group of young, dividing cells in a growing organ. This is an early embryonic meristem from which other developed meristems originate.
Primary meristems: Primary meristems are derivative of Promeristems. This meristem appears early in the life of the plant body that’s why it is called the primary meristem.
Secondary meristems: Secondary meristem appear later than primary meristem. They are cylindrical meristems.
On the basis of position meristems are classified as
1.Apical meristems: Apical meristems are located at the apex of root and shoots. And help in growth of plants in length.
2.Intercalary meristems: in these as the name suggests meristems are intercalated in between mature tissues it means permanent tissues. Intercalary meristems in increase in the length of plants
3.Lateral meristems: The meristems which are present at lateral sides of roots and shoots are called lateral meristems .lateral meristems are found only in those plants in which secondary growth occurs.
Now coming to the question
Intrafascicular cambium is the primary meristem because it appears early in the plant body and contributes to the formation of the primary plant body. An Intrafascicular cambium is lateral in position hence called lateral meristem.
Interfascicular cambium appears later than primary meristem hence they belong to the class of secondary meristem. An interfascicular cambium is lateral in position hence called lateral meristem.

Additional information:
Secondary meristem helps in increasing girth of plants
Primary meristem helps in increasing length of the plants
Apical meristem and intercalary meristems are primary meristems generally lateral meristems are secondary meristems (except Intrafascicular cambium)
Hence the correct option is partially primary and partially secondary (A).

Note: Intrafascicular cambium is the primary meristem. The cells primary meristems are always in state of division
Interfascicular cambium and cork cambium belong to the secondary meristem.
Lateral meristems do not occur in all plants. They occur only in those plants that produce woody axis or show secondary growth.
All plants undergo primary growth but apart from primary growth, most dicotyledonous plants exhibit secondary growth also. Generally secondary growth does not occur in monocots due to the lack of vascular cambium (lateral meristems)in them.
Secondary growth also occurs in stems and roots of gymnosperms also due to presence of lateral meristems.