Callus is

Options

A. Tissue that forms embryo
B. An insoluble carbohydrate
C. Tissue that grows to form embryoid
D. Unorganised actively dividing mass of cells maintained in culture.

Answer

To answer the question "Callus is", we will analyze the options provided and determine the correct definition of callus.

### Step-by-Step Solution:

1. **Understanding Callus**:
- Callus is a type of tissue that forms in plants. It is crucial in the process of tissue culture and regeneration.

2. **Analyzing the Options**:
- **Option A**: "Callus is a tissue that forms embryo."
- This is incorrect because callus itself does not directly form an embryo; it is a precursor tissue.
- **Option B**: "An insoluble carbohydrate."
- This is incorrect as callus refers to a mass of cells, not a carbohydrate.
- **Option C**: "Tissue that grows to form embryo."
- While callus can contribute to the formation of embryos in certain contexts, this description is not specific enough.
- **Option D**: "Unorganized actively dividing mass of cells maintained in tissue culture."
- This is the most accurate description as callus is indeed an unorganized mass of cells that actively divides and can be maintained in a culture environment.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Option D**: "Unorganized actively dividing mass of cells maintained in tissue culture."

### Final Answer:
Callus is an unorganized actively dividing mass of cells maintained in tissue culture (Option D).