The process of anther opening was followed in different species by means of light and electron microscopical techniques, stereo microscopical observation inside living tissues and micromanipulation. From these data and a review of the mainly very old literature on this subject, the opening process is outlined. It consists of the following stages: (1) Expansion of the epidermis and endothecium cells and deposition of U-shaped wall thickenings inside the latter. (2) Enzymatic opening of the septum between two locules. (3) Mechanical rupture of the tapetum. (4) Mechanical opening of the stomium by the centripetal force of the highly turgescent epidermis and endothecium. (5) Outward bending of the locule walls by the centrifugal force of the dehydrating epidermis and endothecium. Steps (4) and (5) clearly reflect the mechanical functions of the two latter tissues. The roles of the other anther tissues and the filament during the earlier stages are discussed.