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periderm per·i·derm (pěr'ĭ-dûrm') or per·i·der·ma (pěr'ĭ-dûr'mə)
The outermost layer of the epidermis of an embryo or a fetus up to the sixth month of gestation. Also called epitrichium.
The outer, protective layers of tissue of woody roots and stems, consisting of the cork cambium and the tissues produced by it. See more at cork cambium.