What are transfusion tissue in gymnosperms?

Explanation

**Step-by-Step Solution:**

1. **Definition of Transfusion Tissue**: Transfusion tissue is a specialized type of tissue found in gymnosperms, particularly around the vascular bundles of their leaves.

2. **Composition of Transfusion Tissue**: This tissue is composed of two main types of cells:
- **Living Cells**: These include parenchyma cells, which have thin, non-lignified cell walls. Parenchyma cells are involved in storage and transport functions.
- **Lignified Tracheids**: These are also present in the transfusion tissue. Tracheids are a type of water-conducting cell that have lignified walls and bordered pits, which facilitate the movement of water and nutrients.

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