The letter a indicates the a cross section of the eudicot root. each letter marks a definite structure. letter a marks the outer layer of the root. letter b marks the small central region of the root. letter c marks a structure that surrounds the central region of the root. letter d marks a cross-like complex in the center of the vascular cylinder, which consists of big oval cells. letter e marks a layer of the vascular cylinder below the endodermis. the letter a indicates the a cross section of the eudicot root. each letter marks a definite structure. letter a marks the outer layer of the root. letter b marks the small central region of the root. letter c marks a structure that surrounds the central region of the root. letter d marks a cross-like complex in the center of the vascular cylinder, which consists of big oval cells. letter e marks a layer of the vascular cylinder below the endodermis. xylem endodermis cortex vascular cylinder epidermis