The acetolysed exine ofBarringtonia calyptrocalyxpollen was investigated by means of light, transmission electron, and scanning electron microscopy of whole and sectioned grains. A simple method of sectioning using a freezing microtome is described. The exine is shown to consist of an endexines. str.which does not stain with basic fuchsin and is more electron-transparent, and an ectexine which stains and is more electron-dense. A fully integrated description is attempted which is shown to be convertible to a numerical code system for computer processing. The structural modifications of the exine are analysed in relation to harmomegathic functioning and it is suggested that they may represent protective closing devices of the apertural area and stress absorbing structures. The evolutionary origin of these structures is discussed briefly andB. calyptrocalyxpollen is shown to be the highly specialized end product of a series which starts with a simple trieolpate pollen type.