Final answer:
Wood is produced by the secondary growth of the xylem, a process mediated by the vascular cambium, which is answer d. The vascular cambium's role is to create a secondary xylem that forms wood inside the plant stem.
Step-by-step explanation:
Wood is produced from the secondary growth of the xylem, which is a process that involves the vascular cambium. This specific type of meristem is responsible for the thickening of the stem in woody plants. The correct answer to the question about what produces wood is d. The vascular cambium.
The vascular cambium generates secondary xylem and phloem which contribute to the plant's thickness growth. As the vascular cambium divides, it forms secondary xylem, consisting of cells such as tracheid and vessel elements, to the inside, and secondary phloem to the outside. The presence of lignin in the cells of the secondary xylem is what makes the tissue hard and wood-like.
In comparison, the apical meristem and root meristem contribute to primary growth which increases the length of shoots and roots respectively, while axillary bud meristem leads to the formation of new shoots or flowers. Mycorrhizae are symbiotic relationships between fungal species and plant roots and do not directly contribute to the wood formation process.