The ascus apex of Ciboria acerina

The apical thickening of the ascus is composed predominantly of a relatively homogeneous and granular ground material laid down between the outer and inner wall layers of the ascus. A cylindrical pore with a central pore plug passes through the apical thickening. The cylinder is continuous with the outer ascus wall layer and extends into the lumen of the ascus. The plug, which obstructs the pore cylinder, consists of a material similar to or identical with the ground material in appearance. There is no outer ascus wall layer overlying the top of the pore plug but at the bottom the inner ascus wall layer separates the pore plug from the ascus lumen beneath. As a result of ascospore dispersal, the pore cylinder becomes everted.