Fundamental (Ground) Tissue System

Strip away the epidermis and the vascular tissue from a plant organ and what remains is the ground (fundamental) tissue system - by definition, everything else, making up the bulk of the plant's structural volume. It is not organised identically in every organ: in a typical dicot stem it differentiates into three named zones (cortex, pericycle and pith), split by their position relative to the vascular tissue into an extrastelar ground tissue lying outside the stele (the cortex and its innermost endodermal layer) and an intrastelar ground tissue lying inside it (the pericycle, medullary rays and pith); a monocot stem, by contrast, never makes this three-way split at all, and its ground tissue instead stays a single continuous mass of parenchyma with vascular bundles simply scattered through it. In leaves the equivalent ground tissue is called mesophyll, and in hydrophytes the cortex itself typically becomes aerenchymatous, packed with air cavities for buoyancy and internal gas t …