Radicle

n. portion of a seedling that develops into the main root; small root-like structure forming the base of a nerve or blood vessel

== In botany, the radicle is the first part of a seedling (a growing plant embryo) to emerge from the seed during the process of germination. The radicle is the embryonic root of the plant, and grows downward in the soil. Above the radicle is the embryonic stem or hypocotyl, supporting the cotyledon(s).
See more at Wikipedia.org...

Noun
1. (anatomy) a small structure resembling a rootlet (such as a fibril of a nerve)
(hypernym) structure, anatomical structure, complex body part, bodily structure, body structure
(part-holonym) nerve, nervus
(classification) anatomy, general anatomy

(n.)
The rudimentary stem of a plant which supports the cotyledons in the seed, and from which the root is developed downward; the stem of the embryo; the caulicle.
  

(n.)
A rootlet; a radicel.
  

Radicle is the diminutive derived from the Latin radix meaning root so it is therefore a little root. A nerve radicle is the smallest extension of a nerve.