We can distinguish 3 major aims in the present research: 1. First we will investigate the distribution, general morphology and ultrastructure of orbicules in a selected number of species belonging to the Rubiaceae, Loganiaceae s.l., Gentianaceae, and Apocynaceae s.l.. To realise this aim, we will use light, scan- ningelectron, and transmission-electron microscopy. A typology will be worked out, based on the general morphology and ultra- structure of the orbicules. The taxonomic importance of this typology will be tested in the Gentianales. 2. In some selected species we will investigate the ontogeny of the orbicules and the tapetum. For this ontogenetical research we will use LM- and TEM-observations of anthers in different stages of development. 3. The localisation of different chemical compounds will be tra- ced in different stages of development of the tapetum cells....