The radicle is the first part of a seedling 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.
Plumule is the young shoot of a plant embryo above the cotyledons, consisting of the epicotyl and often of immature leaves.
Cotyledon is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon may become the embryonic first leaves of a seedling.
The ovule is the structure that gives rise to and contains female reproductive cells. Thus, the correct answer is an option (a) 'Plumule'.