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How does the radicle guide a germinating seedling into the soil?
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seed
Fruit and seeds of the southern magnolia (Magnolia grandiflora). The fruit is an aggregate of follicles, and each follicle bears a single red seed.
The radicle, which is the primary root of a germinating seed, guides the seedling into the soil primarily through a response to gravity known as positive geotropism.12
Because the radicle is positively geotropic, it is biologically oriented to grow downward into the earth. This directional growth ensures that the seedling establishes a firm anchor in the soil, allowing it to access necessary water and nutrients while the shoot, or plumule, grows in the opposite direction (negative geotropism) to reach the surface.12