Pith is a substance that's found in vascular plants. It consists of soft, spongy parenchyma cells, and is located in the center of the stem in eudicots (both herbaceous and woody) and in the center of the roots in monocots. It is encircled by a ring of xylem (woody tissue), and outside that, a ring of phloem (bark tissue). In some plants the pith is solid, but for most it's soft. A few plants, such as walnuts, have distinctive chambered pith with numerous short cavities. The word comes from th… (More on Pith)