Histogen is

Options

A. secondary meristem forming a specific tissue
B. intercalary meristem forming a specific
C. promeristem forming a specific tissue
D. none of the above.

Answer

**Step-by-Step Solution:**

1. **Understanding Histogen**: Histogen refers to a concept in plant anatomy that is associated with the histogen theory, which was proposed by the scientist Hainston in 1870.

2. **Histogen Theory**: According to the histogen theory, the root apex is divided into three distinct regions, each responsible for forming different tissues in the root.

3. **Identifying the Three Regions**:
- **Dermatogen**: This is the outermost layer that forms the epidermis (or epiblema) and the root cap in dicots.
- **Periblem**: This middle layer is responsible for forming the cortex and the endodermis.
- **Pleurome**: This innermost layer forms the pericycle, vascular strands, and pith.

4. **Clarifying Misconceptions**: It is important to note that histogen is not a secondary meristem. Instead, it is classified as a pro-meristem, which is involved in the early stages of plant development.

5. **Conclusion**: Based on the histogen theory, histogen is a pro-meristem that contributes to the formation of specific tissues in the root.

**Final Answer**: Histogen is a pro-meristem that forms specific tissues in the root apex, including the epidermis, cortex, endodermis, pericycle, vascular strands, and pith.

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