Adaptability of Scanning Electron Microscopy to Studies of Pollen Morphology

We have explored methods to achieve excellent results in study of the pollen grain wall by using only one electron microscope, the scanning electron microscope (SEM). While the secondary electron imaging mode , the most common in use, has great value in characterizing the exine surface it is possible to obtain a more comprehensive representation of pollen grain walls by expanding the capability of the secondary mode and making use of backscatter and transmission imaging detectors. In this way information is obtained about internal exine features that are likely to be more stable phylogenetically than the generally late-to-form surface structure. We illustrate the usefulness ofnatural and induced fractures, cryornicrotorny, thin-section examination, section deplasticization, localized acetolysis and pollen erosion by ionic bombardment in imaging exine structure. Techniques for expand ing the use of SEM in taxonomic stud ies of mature pollen grain walls are outlined in flow chart sketches and illustrated with numerous examples from angiosperm pollen.