Grafted walnuts show callus growth from the cambium, and also from the pith of stems and the endodermis of the root.
"Northern Nut Growers Association Report of the Proceedings at the Thirty-Eighth Annual Meeting" by Northern Nut Growers Association
Root-hair; 2. piliferous layer; 3. cortex; 4. endodermis; 5. pericycle; 6. xylem; 7.
"A Handbook of Some South Indian Grasses" by Rai Bahadur K. Ranga Achariyar
ENDODERMIS, the innermost layer of the cortex.
"The New Gresham Encyclopedia" by Various