The common occurrence of incompletely developed pollen of Eupatorium (Compositae: Eupatorieae)

Mature anthers of Eupatorium serotinum Michx., E. coelestinum L. and E. purpureum L. (Compositae: Eupatorieae) contain both loose mature pollen grains and acetolysis-resistant extratapetal sacs enclosing clusters of immature pollen. Many sacs contain incompletely developed pollen grains that differ in size diameter, with spines of varying lengths and degrees of acuity and with colpal areas having narrow to markedly protracted margins. We presume that all nutrients for pollen development within sacs come from plasmodial tapetum included therein. Thus, pollen in portions of the sac or in isolated sacs with inadequate plasmodial tapetum may be incompletely developed. Such partial development may result from stress, e.g. insufficient nutrients and water. While our data are from three species of Eupatorium, we have long noted the syndrome in other Eupatorieae and other tribes in the Compositae. Curtailing supplies for development of some portions of an anther could be an evolutionary strategy for survival of the species through periods of stress.     

The Use of Osmium-Thiocarbohydrazide for Structural Stabilization and Enhancement of Secondary Electron Images in Scanning Electron Microscopy of Pollen

Pollen grains stained in a sequence of osmium (O) and thiocarbohydrazide (T) solutions (collectively known as OTOTO) appear structurally stable and undistorted in the scanning electron microscope (SEM), and usually do not require special drying. In fact, OTOTO can be regarded as another special drying method in palynology. This sequential incubation also strikingly increases the electrical conductivity of pollen grains in the SEM. Compared to standard sputter-coating or vacuum evaporative procedures, OTOTO reduces charging and yields secondary electron images with significantly higher resolution.