In Lathyrus aphaca (wild pea) all the leaflets are modified in the tendrils.

Answer

### Step-by-Step Solution:

1. **Understanding the Plant Structure**:
- In Lathyrus aphaca (wild pea), the leaves are modified into tendrils.
- Tendrils are specialized structures that help plants climb by wrapping around supports.

2. **Definition of Tendrils**:
- Tendrils are thread-like, sensitive structures that can coil around objects to provide support for climbing plants.

3. **Types of Tendril Modifications**:
- Tendrils can be modified from various parts of the plant, including:
- Whole leaves
- Leaflets
- Petioles (the stalk that attaches the leaf to the stem)
- Rachis (the main axis of a compound leaf)

4. **Specific Case of Lathyrus aphaca**:
- In the case of Lathyrus aphaca, the entire leaf is modified into a tendril.
- This adaptation allows the plant to climb effectively.

5. **Function of Tendrils**:
- The primary function of tendrils is to assist in climbing, which is crucial for plants that grow in competitive environments for sunlight.

6. **Compensation for Photosynthesis**:
- Since the leaves are modified into tendrils, the plant must compensate for photosynthesis.
- In Lathyrus aphaca, the stipules (small leaf-like structures at the base of the leaf) become foliaceous (leaf-like) to perform photosynthesis.

7. **Conclusion**:
- The statement that in Lathyrus aphaca all leaflets are modified into tendrils is true.
- The entire leaf structure is adapted for climbing, while the stipules take over the photosynthetic function.