Preface 1. Introduction 2. Interactions of developing organs 3. Hormones as correlative agents 4. Callus and tumour development 5. The polarization of tissues 6. The canalization of vascular differentiation 7. Cell lineages 8. Stomata as an example of meristemoid development 9. Expressions of cellular interactions 10. Apical meristems 11. The localization of new leaves 12. A temporal control of apical differentiation 13. Generalizations about pattern formation.