Atlas of plant and animal histology

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Virtual microscopy


Image: elderberry secondary stem stained with safranin / Alcian blue. The secondary grow is not well-developed yet.

Epidermis: it is the outermost layer of the stem. In this case, the periderm tissues generated during the secondary grow are pushing the epidermis out, although it can still be observed. It later stages of secondary grow, the epidermis is lost.

Cork: it is the outer layer of the stems with secondary grow. In this case, the epidermis from the primary grow is still present. Corks cells are produced by the fellogen meristem and die to fulfill their protecting role.

Fellogen: or cork cambium, is the meristem that produce cork outward and felloderm inward. The fellogen is found more peripheral than the vascular cambium, and it is present in stems with secondary grow.

Felloderm: it is the layer of cells differentiated inwardly from the fellogen. They are parenchimatic cells that can be usually observed as radial rows.

Lenticel: it is a periderm modification that allows the exchange of gases between the stem and the environment. Lenticels appear as interruptions in the surface of the stem.

Collenchyma: it is the supporting tissue found below the periderm. Collenchyma cells show cell walls stained in red. In this case, it is laminar collenchyma.

Cortical parenchyma: it is the parenchyma between the vascular tissue and peridermis/collenchyma.

Secondary phloem: it is the vascular tissue specialized in transporting organic molecules. In this case, secondary phloem is a strip of tissue with small cells with thin cell wall stained in blue. It is found below the cortical parenchyma, although some sclerenchyma fibers can be seen between the cortical parenchyma and the secondary phloem.

Vascular cambium: it is the meristem found between the secondary phloem and the secondary xylem. By proliferation and differentiation, the vascular cambium gives rise to the secondary phloem outward and the secondary xylem inward.

Secondary xylem: it is the vascular tissue specialized in transporting water and minerals. The secondary xylem consists of large conducting cells with thick cell walls stained in red, sclerenchyma fibers and parenchyma cells.

Primary xylem: it is the remaining xylem of the stem primary grow. The primary xylem is not functional and appears as small groups in the deeper surface of the secondary xylem, where the primary grow vascular bundles were located.

Pith: it is the largest region of the stem, which is occupied by parenchyma tissue consisting of large cells with cell walls stained in blue.