Rhizophore of Selaginella is organ suigeneris .

Answer

### Step-by-Step Solution:

1. **Understanding the Term "Organ Sui Generis":**
- The term "organ sui generis" refers to a unique organ that has characteristics distinct from typical organs. It was introduced by scientist J.C. Shrout.
- This term is used to describe an organ that serves as an intermediate structure between two different types of organs, in this case, between roots and shoots.

2. **Identifying the Rhizophore in Selaginella:**
- The rhizophore is a specialized structure found in the plant Selaginella.
- It functions as a transitional organ that exhibits features of both roots and shoots.

3. **Characteristics of the Rhizophore:**
- The rhizophore does not bear leaves, which is a characteristic typically associated with shoots.
- It exhibits positive geotropism, meaning it grows towards gravity, similar to roots.

4. **Conclusion:**
- Due to its unique characteristics that combine features of both roots and shoots, the rhizophore of Selaginella is classified as an "organ sui generis."