Tracheids and vessels are present in all except Cycas

Tracheids and vessels are two types of conducting cells found in the xylem tissue of vascular plants. They play a crucial role in the transportation of water and minerals from the roots to the rest of the plant. However, tracheids and vessels are not present in all vascular plants.

Tracheids
- Tracheids are elongated cells with tapered ends that are found in the xylem tissue of plants.
- They are dead cells with thick secondary cell walls that are lignified, providing strength and structural support to the plant.
- Tracheids are responsible for the upward movement of water and minerals through their interconnected pits.
- They are present in all vascular plants, including ferns (Marselia), horsetails (Equisetum), and gymnosperms like gnetophytes (Gnetum).

Vessels
- Vessels are another type of conducting cells found in the xylem tissue of plants, specifically in angiosperms (flowering plants).
- Unlike tracheids, vessels are made up of multiple cells called vessel elements that are stacked end-to-end.
- Vessel elements have perforations on their end walls called perforation plates, allowing for efficient water flow.
- Vessels are wider and more efficient in water transport compared to tracheids.
- They are absent in non-flowering seed plants like cycads (Cycas).
- Cycads have tracheids but lack vessels, making them the exception in terms of the presence of vessels.

Summary
- Tracheids and vessels are two types of conducting cells found in the xylem tissue of vascular plants.
- Tracheids are present in all vascular plants, including ferns (Marselia), horsetails (Equisetum), gymnosperms like gnetophytes (Gnetum), and angiosperms (flowering plants).
- Vessels, on the other hand, are absent in non-flowering seed plants like cycads (Cycas), making them the exception.