In the seeds of cereals, the outer covering of endosperm separates the embryo by a protein-rich layer called:

The correct option is Aleurone layer.

Step-by-step Explanation:

1. In monocotyledonous seeds, particularly those of cereals like maize and wheat, the seed is generally endospermic. The endosperm acts as a major food storage tissue that nourishes the developing embryo.

2. The embryo is relatively small and lies in a groove at one end of the endosperm.

3. The outer covering of the endosperm separates the embryo by a distinct, specialized proteinaceous layer.

4. This protein-rich layer is called the aleurone layer. It plays an important physiological role during seed germination by synthesizing and secreting hydrolytic enzymes (such as amylase) that break down starch stored in the endosperm into sugars for the growing embryo.

5. Let's briefly define the other options to understand why they are incorrect:
- Coleoptile: A protective sheath that encloses the young shoot (plumule) in cereal seedlings.
- Coleorhiza: A protective sheath that encloses the young root (radicle) and root cap in cereal seeds.
- Integument: The outer cell layer(s) of an ovule that develops into the seed coat after fertilization, rather than a layer separating the endosperm and the embryo within the seed.