Phloem location in dicot roots

Steps:

• Recall that herbaceous dicot roots have a central vascular cylinder with xylem forming a star-shaped core.
• Note phloem occurs in discrete patches between the xylem arms, outside the xylem but inside the pericycle.
• Examine diagrams for this radial arrangement with phloem not surrounding xylem completely.
• Select the diagram matching phloem between xylem ridges.

Why D is correct:

• Diagram D shows phloem patches alternating with xylem arms in the stele, matching the dicot root's exarch xylem and phloem definition.

Why the others are wrong:

• A places phloem centrally, incorrect as xylem occupies the core.
• B shows phloem surrounding the entire vascular bundle, typical of stems not roots.
• C depicts phloem inside xylem arms, violating the standard dicot root layout.

Final answer: D