it encounters light. If further elongation is required (for example, if the seeds are planted or covered too deeply), the region of the shoot below the coleoptile begins to elongate. This region is called the mesocot- yl. Usually, it does not develop in water-seeded rice. The mesocotyl originates from the embryo area and merges with the coleoptile. The mesocotyl and cole- optile can elongate at the same time. They are some- times difficult to tell apart. Usually, the mesocotyl is white, and the coleoptile is off-white and slightly yel- lowish. Shortly after the coleoptile is exposed to light, usually at the soil surface, it stops elongation. The appearance of the coleoptile signals emergence. From