Half of an acorn, cut lengthwise, filled by the very thick cotyledons, the base of which encloses the minute caulicle.

Embryo taken out whole and unfolded; the broad and very thin cotyledons notched at summit; the caulicle below.

The end which almost touches the seed coat is caulicle, the other end belongs to the solitary cotyledon.

A secondary office is to hold the seed firmly, so that the caulicle can enter the ground.