The cactus has a specialized fleshy stem and it's leaves function only for protection. which plant tissues most likely makes up the stem?

The correct answer is vascular tissues.  

Vascular tissues most likely form the stem. The prime vessels observed on the vascular tissue are the phloem and the xylem. These two tissues function as an element for the conduction of nutrients and water within the stem.  

The xylem transports some nutrients and water from the roots, while the phloem transports the soluble organic constituents, which were generated at the time of photosynthesis from the leaves.  

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