Internal Structure of Orchid Root: Most orchids are epiphytes. They have hanging aerial roots. Their anatomy is different from other monocotyledonous roots and is as follows:
1. Velamen:
- It is the outermost tissue of the root.
- The cells of this tissue are large, closely packed, with fibrous thickenings.
- These are dead cells. These cells are filled with air in dry season and during rains these cells absorb water.
- Velamen is like a multilayered epiblema.
- The outermost layer of velamen is called limiting layer. It is cuticularized.
2. Exodermis:
- It is the outermost layer of the cortex.
- The lateral walls of the exodermal cells are thickened.
- Passage cells are found here and there.
3. Cortex:
- The cortex is made up of thin walled parenchymatous cells.
- The innermost layer of the cortex is endodermis.
- All tissues enclosed by the endodermis are called stele.
4. Pericycle:
- It is one layered tissue on the inner side of endodermis.
5. Conjunctive tissue:
- It is the parenchymatous tissue surrounding and in between the vascular bundles.
6. Vascular bundles:
- Vascular bundle are radial. Xylem and phloem are present as alternate patches and are situated in a ring.
- Vascular bundles are more than six. Xylem is exarch.