One of the following is not the causal organism for ringworm.

Options

A. Microsporum
B. Trichophyton
C. Epidermophyton
D. Macrosporum

Explanation

To determine which organism is not a causal agent for ringworm, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for an organism that does not cause ringworm, which is a fungal infection.

2. **Identify the Causal Organisms**: Ringworm is primarily caused by certain types of fungi. The common genera associated with ringworm include:
- **Microsporum**
- **Trichophyton**
- **Epidermophyton**

3. **Analyze the Options**: The options given are:
- 1) Microsporum
- 2) Trichophyton
- 3) Epidermophyton
- 4) Macrosporum

4. **Determine the Incorrect Option**:
- **Microsporum**, **Trichophyton**, and **Epidermophyton** are all known to cause ringworm.
- **Macrosporum**, on the other hand, is not associated with ringworm infections. Instead, it is an ectomycorrhizal fungus that affects vascular plants.

5. **Conclusion**: The organism that is not a causal agent for ringworm is **Macrosporum** (Option 4).

### Final Answer:
The organism that is not a causal organism for ringworm is **Macrosporum** (Option 4).

---