Fig. 3.2-7. Transverse section of pine wood (Pinus). This is one of the secretory ducts in pine that produce the pitch that you may have seen oozing from a wound in a living tree or dripping from a piece of pine lumber. Although these are secretory parenchyma cells, they do not have dense protoplasm like that of ducts in Artemisia (Fig. 3.2-6). These parenchyma cells are rather large and pillowy, and the walls that faces the duct lumen are not smooth and taut but instead are undulate, so they do not show a clean profile. The outer walls of each cell are somewhat thicker than is typical of parenchyma cells.