Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which in some cases can store starch. In eudicotyledons, pith is located in the center of the stem. In monocotyledons, it extends only into roots. The pith is encircled by a ring of xylem; the xylem, in turn, is encircled by a ring of phloem.
Elder shoot cut longitudinally to show the broad, solid pith (rough textured, white) inside the wood (smooth, yellow tinged). Scale in millimeters.
The tiny central dark spot (diameter: about 1 millimeter (0.039 in)) in this yew wood is the pith.
In biology, tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Tissues occupy a biological organizational level between cells and a complete organ. Accordingly, organs are formed by the functional grouping together of multiple tissues.
Microscopic view of a histologic specimen of human lung, consisting of various tissues: blood, connective tissue, vascular endothelium and respiratory epithelium, stained with hematoxylin and eosin.
Cross section of 2-year-old Tilia americana, highlighting xylem ray shape and orientation
Cross section through skeletal muscle and a small nerve at high magnification (H&E stain)
Xavier Bichat (1771–1802)
