1. (fibrous layer) The subepidermal layer of the *anther
wall in angiosperms. The cells of the endothecium often develop thickenings on the anticlinal and inner tangential walls as the anther matures, which are believed to aid in anther dehiscence.
2. The inner layer of cells in the young sporophyte of bryophytes, giving rise to the columella and (except in Sphagnum) sporogenous tissue. Compare amphithecium