A coleoptile is a pointed protective sheath that covers the emerging shoot in monocotyledons such as grasses. It is the first leaf of a monocotyledon that forms a protective sheath about the plumule. Coleoptiles consist of very similar cells that are all specialized for fast stretch growth. They do not divide but increase in size as they accumulate more water. Coleoptiles also have water vessels along the axis to provide a water supply. When a coleoptile reaches the surface, it stops growing, and the flag leaves penetrate its top, continuing to grow along. The wheat coleoptile is most developed on the third day of germination (if in the darkness) .

The coleoptile acts as a hollow organ with stiff walls, surrounding the young plantlet and the primary source of the gravitropic response. It is ephemeral, resulting in rapid senescence after the shoot emerges. The length of the coleoptile can be divided into an irreversible fraction, length at turgor pressure 0, and reversible fraction, or elastic shrinking. Changes induced by white light increase water potential in epidermal cells and decrease osmotic pressure, which resulted in an increase in the length of the coleoptile.

In summary, a coleoptile is a protective sheath that covers the emerging shoot in monocotyledons such as grasses. It is the first leaf of a monocotyledon that forms a protective sheath about the plumule. Coleoptiles consist of very similar cells that are all specialized for fast stretch growth, and they have water vessels along the axis to provide a water supply. When a coleoptile reaches the surface, it stops growing, and the flag leaves penetrate its top, continuing to grow along. The coleoptile acts as a hollow organ with stiff walls, surrounding the young plantlet and the primary source of the gravitropic response.