What comprises of bark in a tree?

Explanation

### Step-by-Step Solution:

1. **Understanding Bark**: Bark is the outer protective layer of a tree. It is important to understand what constitutes bark in the context of a tree's anatomy, especially in old dicotyledonous (dicot) stems.

2. **Secondary Growth in Dicot Stems**: Dicot plants undergo secondary growth due to their open vascular bundles. This means that they can increase in thickness over time, which is a characteristic of woody plants.

3. **Formation of Vascular Tissues**: During secondary growth, two main types of vascular tissues are formed: secondary xylem (wood) and secondary phloem. These tissues are produced by the vascular cambium, a layer of meristematic tissue.

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