1. <dermatology> The basal layer of the mammalian epidermis contains cells that undergo repeated divisions. The cells outwards from a particular basal cell are often derived from this cell or a nearby one so that columns of cells exist running outwards from the stem cell in the basal layer from which they were derived. Such columns of cells are referred to as proliferative units.

2. <biology> Outer epithelial layer of a plant or animal. May be a single layer that produces an extracellular material (as for example the cuticle of arthropods) or a complex stratified squamous epithelium, as in the case of many vertebrate species.

(11 Mar 2008)