|sexual form of a haploid plant in the alternation of generations|
|variation in an organism's life cycle of dissimilar reproductive forms|
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.