Short answers, pulled from the story.
The vascular cambium is a microscopic layer of cells responsible for the girth of the world's largest trees. It exists in the stems and roots of many plants to drive secondary growth in dicots and gymnosperms. This tissue acts as a factory that builds the infrastructure required for water and food transport without moving anything through the plant itself.
In woody plants, vascular bundles fuse to form a complete tube that allows the tree to expand in diameter year after year. In herbaceous plants, this tissue appears as vascular bundles arranged like beads on a necklace, forming an interrupted ring inside the stem. The continuous ring in woody plants pushes primary xylem and primary phloem apart as new layers are added.
Auxin hormones stimulate mitosis and cell production while regulating both the interfascicular and fascicular cambium. Gibberellin stimulates cambial cell division and regulates the differentiation of xylem tissues without affecting the rate of phloem differentiation. Cytokinin hormone regulates the rate of cell division rather than the direction of cell differentiation.
Vascular cambia are absent in five specific angiosperm lineages including Nymphaeales, Ceratophyllum, Nelumbo, Podostemaceae, and monocots. These plants have independently lost the ability to produce them and must rely on primary growth mechanisms to increase in size. This absence represents a significant evolutionary divergence where structural support is achieved through different biological pathways.
The cambium of most trees is edible and has served as a hidden food source that sustained human populations through harsh winters. In Scandinavia, it was historically used as a flour to make bark bread, a survival food that allowed communities to endure periods when grain was unavailable. This tissue was ground into a fine powder and baked into loaves to create a staple carbohydrate.