The document discusses periderm, the protective layer of bark that forms in plants. It is composed of three layers: the phellogen or cork cambium, the phellem or cork layer, and the phelloderm. The document describes where the phellogen layer originates in different plant species, either just under the epidermis or deeper in the stem tissue. It also discusses lenticels, which allow gas exchange, and rhytidome, the layers of old periderm. Commercial cork is harvested from cork oak trees.

1. Periderm

2. Periderm
• Phellogen – cork cambium
• Phellem – cork
• Phelloderm – parenchyma like tissue

3. Periderm, Cork, and Bark
• Bark = all the tissues outside of the
vascular cambium
– Inner Bark includes all the tissues from the
secondary phloem outward to the phelloderm
(or phellogen)
– Outer Bark includes the periderm and all the
tissue outside of it
• Rhytidome
– all the successive periderms that develop
– bark external to the last formed periderm

4. Periderm developing on a branch

5. Development of Periderm

6. Periclinal divisions of sub-epidermal cells
leads to the development of phellogen

7. In Quercus alba, the phellogen originates in
sub-epidermal cells
Phellogen has produced 4 layers of phellem (cork) and one layer of phelloderm

8. In Solanum (nightshade), the phellogen
arises from the epidermis

9. Phellogen in Clematis originates deep in stem tissue from
phloem parenchyma cells below the fiber caps
Phellogen (cork
cambium)
Vascular cambium

10. In grape vines, the phellogen also
originates in the primary phloem

11. Periderm with tannins
Tannins deter insects and other animals from feeding on bark, adding to
the protective capacity of bark.
Oak Clusia

12. Tilia periderm

13. Lenticels

14. Lenticels in moonseed form prior to
periderm formation
Cuticle

15. Lenticel in Aristolochia

16. Sambucus lenticel

17. Lenticel in ivy stem

18. Rhytidome

19. Robinia rhytidome

21. Pine Walnut Paper birch Crepe myrtle
White ash Sweetgum Tilia White Oak

22. Commercial cork is
obtained from Quercus
suber, the cork oak tree

24. Harvesting and Regrowth