In this survey of root tip structure in vascular plants it is found that the three dermal layers, epidermis, hypodermis and endodermis, and the root cap, except where a calyptrogen is present, are ...

The xylem is surrounded by meristematic or parenchymatous cells through which small branches of abnormal phloem are interspersed. In stems of clover, tumors are also initiated by tangential divisions ...