1. The larger roots of Ipomoea batatas Lam. are polyarch, chiefly pentarch and hexarch. 2. Secondary thickenings occur in the usual way and there is formed a massive structure of secondary xylem. 3. Secondary cambiums are organized around strands of xylem and phloem which are separated by thin-walled parenchymatous cells. The primary and secondary cambiums are capable of forming xylem and phloem in isolated strands. One may reasonably expect that, if the conditions for growth are especially favorable, the secondary cambiums may be organized earlier. 4. A section of a mature tuber shows a structure consisting chiefly of parenchyma, and mingled with the parenchyma are strands of xylem, which consist of one to several vessels, and may or may not be accompanied by phloem. Each strand is surrounded by a cambium. There may also be seen strands of phloem unaccompanied by xylem. This structure may be definitely traced back to the radial protostele.