In woody dicots, the strip of cambium present between the primary xylem and phloem is the interfascicular cambium. The cells of the medullary rays adjoining the interfascicular cambium become meristematic and form the interfascicular cambium. This results in the formation of a continuous cambium ring. The activation of the cambium ring results in the cut off new cells. The secondary phloem is formed by the cells which are cut off towards the periphery cells. The secondary xylem is formed by the cells cut off towards the pith. The cambium being more active on the inner side, the amount of the secondary xylem produced is more than that of the secondary phloem. At some places the cambium forms the narrow band of parenchyma called the secondary medullary rays. These medullary rays pass through the secondary xylem and secondary phloem in the radial directions. 

The secondary growth in plants:
i. Increases the girth of plants,
ii. Increases the amount of water and nutrients to support the growing number of leaves.
iii. Provides support to plants.

We would ascertain whether the given stem is a monocot stem or dicot stem by looking at some characteristics which are unique as to the particular type.
The dicots stem is characterised by the following unique characters:
i. vascular bundles are arranged in a
ii. Each vascular bundle is conjoint, collateral, and open.
iii. Medullary rays are present between the vascular bundles.
iv. Pith is present.
If these characters are observed in the given stem, then it a dicot stem

The monocot stem are characterised by the following unqiue characteristics:
1. Vascular bundles are scatttered.
2. Each vascular bundle is conjoint, collateral, and closed vascular bundles. 
3. Medullary rays are absent. 

(a) Monocot root and dicot root:

(b) Monocot stem and dicot stem:

Meristems are specialised regions of active cell division in plants. The meristems represent the regions of growth. Growth is largely restricted to the meristem regions of the plant.  Depending on their location the meristems are of three types.

(i) Apical meristem:
These meristems are present at the tips of the roots and shoots. The shoot apical meristem is present at the tip of the shoots and its active division results in the elongation of the stem and formation of new leaves. The root apical meristem helps in the elongation or growth of roots. They are primary meristems as they appear early in the plant life. 

(ii) Intercalary meristem:
These are present between the masses of mature tissues present at the bases of the leaves of grasses. It helps in the regeneration of grasses after they have been grazed by herbivores. They are primary meristem.

(iii) Lateral meristem:
It appears in the mature tissues of roots and shoots. It is called the secondary meristem as it appears later in a plant's life. It helps in adding secondary tissues to the plant body and in increasing the girth of plants. Examples include fascicular cambium, inter-fascicular cambium, and cork cambium.

The scattered vascular bundles surrounded by sclerenchymatous bundle sheaths and the absence of the phloem parenchyma is unqiue to the monocot stem. Thus, the specimen is of a monocot stem.