Callus: Differentiation vs organisation

There is considerable variability in the extent and type of cellular differentiation in callus cultures. A homogeneous callus consisting entirely of parenchyma cells is rarely found. Cytodifferentiation occurs in the form of tracheary elements, sieve elements, suberized cells, secretory cells, and trichomes.
	Different cell types in a cell culture

Small area of dividing cells form meristemoids or vascular nodules
that may become centers for the formation of shoot apices, root
primordia, or incipient embryos.

Shoot (caulogenesis) (a) and root development (b & c) on callus of Hypoxis

Callus: Scheme for organogenesis,
embryogenesis and cell culture