Pit fields in fusiform initials of walnut

Cambium of walnut (Juglans nigra) showing the living content of both fusiform and ray initials. The radial (anticlinal) walls of the fusiform cells clearly show primary pit fields.

Examination of this micrograph shows evidence of oblique anticlinal walls which establish a new divisional plane (arrow) for growth. It is the anticlinal division of cells of the vascular cambium that gives rise to new vascular cambium, and therefore increases the circumference of the tissue.