Ultrastructure of the ?fringe-layer?, the innermost epidermis of cotton seed coats

Abstract

The inner epidermis of the inner integument of cotton seed coats (fringe-layer) and the cuticles between this cell layer and the nucellus were examined in the light and electron microscope at different times of their development. The cells of the fringe-layer contain only small vacuoles and their cytoplasm is densely packed with organelles and free and membrane-bound polysomes. The lateral walls contain many plasmodesmata. At the time when the fruit capsules stop growing, the fringe-cells produce a cell wall labyrinth, resembling that of transfer cells. The cell wall labyrinth is restricted to the lateral walls. The differentiated state of the fringe-cells is short-lived. At about the time of elaboration of the cell wall labyrinth most of them become progressively vacuolated, lignify, and lose their cytoplasmic constituents. The development of the fringe-layer is well correlated with other developmental events in the inner integument, but not with the filling of embryo and endosperm with reserve substances.