radicle

Radicle is the embryonic root of a plant. In seed plants the radicle is the part of the embryo that develops into the primary root, the first root to emerge during germination. It anchors the seedling and begins the uptake of water and nutrients, establishing the root system on which the mature plant depends.

During germination, moisture activates metabolism and the radicle protrudes through the seed coat, typically growing downward under the influence of gravity (gravitropism). In most dicot seeds, the radicle enlarges to form the primary root, which then produces lateral roots. In many monocot seeds, the radicle may die early and a fibrous root system develops from the stem; in grasses, the tip of the radicle is often protected by a coleorhiza as it emerges.

Etymology: the term radicle comes from Latin radicula, a diminutive of radius, meaning little root. In botany, radicle is contrasted with plumule, the embryonic shoot that develops into the aboveground part of the plant.

Radicle development can be affected by seed vigor, temperature, moisture, and soil conditions, and abnormal radicle growth is sometimes observed in seeds afflicted by disease or environmental stress.