Bark

'Bark' is the everyday term applied to everything outside the vascular cambium of a stem - the periderm, the cortex, the primary phloem and the secondary phloem together, considered as one functional unit rather than as separate tissues. Bark performs several protective jobs at once: it shields the plant from parasitic fungi and insects, prevents water loss through evaporation, buffers the plant against external temperature variation, and is naturally insect-repellent, decay-proof and fire-resistant, in addition to being a source of certain drugs and spices. Within the bark, the two living components have different roles - the phloem cells conduct food, while the secondary cortical cells are mainly used for storage. How the bark actually looks and behaves depends on how the phellogen (cork cambium) itself develops: if the phellogen forms a complete, continuous cylinder around the stem, the bark it produces is a ring bark, which does not peel off as the stem grows (Quercus, oak, is the textbook example); if instead the phell …