Sequential staining to assess viability and starch content in individual pollen grains.

Individual pollen grains may be assessed for viability and starch content by dusting a sample onto drops of an aqueous medium containing fluorescein diacetate and potassium iodide, and allowing them to accumulate free fluorescein for ten minutes. They are then illuminated with ultraviolet or blue light and photographed to record the proportion that fluoresce, as an index of viability. The preparation is exposed to iodine vapor and the same field of view rephotographed in bright field illumination to record starch content.