A stand of forest trees shares a single underground fungal network — the "wood wide web" — built from mycorrhizal hyphae that colonize each tree's roots. Start the exchange to watch the two-way trade that keeps the symbiosis running: trees send carbon sugars from photosynthesis down into the fungus, and the fungus sends back water and phosphorus drawn from far more soil than roots alone could reach. Select a tree to see its own flows highlighted, including the extra carbon the shaded mother tree routes through the network to support younger saplings that can't yet make enough sugar of their own.