Immediately inside the epidermis of a eudicot stem is the pith.

Epidermis

The outer layer of cells covering an organism, particularly the surface epithelium of the skin of animals or the outermost layer of plants.

Eudicot Stem

The stem structure of a eudicot plant, characterized by the arrangement of vascular bundles in a ring.

Pith

The central core of the stems of vascular plants, composed of soft, spongy parenchyma cells that store and transport nutrients throughout the plant.