Moss leaf. Light micrograph of the tip of a young leaf of an unidentified species of moss. Most mosses have little or no internal differentiation of tissues, with leaves one cell thick. The bumpy appearance of the leaf cells (upper left) is due to the presence, in each cell, of several disc- shaped chloroplasts, the sites of photosynthesis. Elongated cells on the outer edge also contain scattered chloroplasts. Magnification: x250 at 35mm size.