Xylem And Phloem Structure

Step 1: Concept
Vascular bundles in dicot stems are characterized by the presence of cambium.
Step 2: Meaning
"Collateral" refers to xylem and phloem being on the same radius. "Open" refers to the presence of cambium, which allows for secondary growth.
Step 3: Analysis
In monocots, cambium is absent, making the bundles "closed". Since cambium is present here, it is an open bundle.
Step 4: Conclusion
Hence, the correct term is collateral open.
Final Answer:(A)

The correct option is (D) :Phloem.