The glands that secrete hormones comprise the endocrine signaling system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell (autocrine or intracrine signalling) or nearby cells (paracrine signalling).
A fen is one of the main types of wetland, the others being grassy marshes, forested swamps, and peaty bogs. Along with bogs, fens are a kind of mire. Fens are usually fed by mineral-rich surface water or groundwater.
A fen is similar to a bog, except a fen gets water not just from rain and snow, but also from groundwater and water running down slopes. Groundwater and water running down slopes bring lots of nutrients, so a fen is able to support more types of plants than a bog.