Image: secondary stem of a gymnosperm, pine, stained with safranin / Alcian blue.
Periderm: it is the outermost layer of the secondary stem. From the surface to the inner part, it is made up of three layers: cork, phellogen and pheloderm. Periderm is not much developed in this image, and the three layers are hardly visible.
Resiniferous canals: they are ducts containing resin. The resin is produced by the parenchyma cells that form the walls of the ducts. Resiniferous canal are observed in all parts of the stem, excepting the medulla and periderm.
Radiomedular parenchyma: it is a tissue organized in layers of parenchyma cells, perpendicular to the stem surface, and found in both vascular tissues: secondary xylem and secondary phloem. Radiomedular parenchyma communicates the deeper and the more superficial regions of the vascular tissue.
Cortical parenchyma: it is the layer of parenchyma cells found between the periderm and the secondary phloem.
Secondary phloem: it is the vascular tissue specialized in transporting organic molecules. The secondary phloem form a continuous layer of tissue between the cortical parenchyma and the vascular cambium.
Vascula cambium: it is the meristem located between the secondary phloem and the secondary xylem. Vascular cambium cells proliferate and differentiate into phloem cells outward and xylem cells inward.
Secondary xylem: it is the vascular tissue specialized in transporting water and minerals. The secondary xylem is made up of large cells with red lignified cell walls. In this image, several growth rings can be observed. As the stem girth grows, the number of rings increases one per year, and the proportion of xylem progressively increases. The wood is largely secondary xylem.
Pith: the central region of the stem consists of parenchyma cells.