How do stems turn into wood?

Stems turn into wood through a process called secondary growth, primarily occurring in vascular plants. This involves the activity of the cambium, a layer of actively dividing cells that produces new layers of xylem (wood) and phloem (bark). As the xylem cells mature, they become lignified, which gives wood its strength and durability. Over time, the accumulation of these layers results in the thickening of the stem, transforming it into wood.