Final answer:
The branch roots and part of the vascular cambium of dicots arise from the pericycle in the root's vascular tissue.
Step-by-step explanation:
The branch roots and part of the vascular cambium of dicots arise from the pericycle, which is the outermost cell layer of the root's vascular tissue. The vascular cambium is a cylinder of cells that originates from undifferentiated cells produced by the apical meristem, located between the xylem and phloem. The pericycle can give rise to lateral roots, while the vascular cambium is responsible for producing new vascular tissue and promoting radial expansion in stems and roots.