Abstract
The exine of S. ionantha pollen is uniformly granular when fixed for 24 hours with 1% OsO4 or when fixed with 10% formaldehyde (for less than 12 hours) followed by OsO4. Increasing the time of exposure to formaldehyde results in a slightly amorphic-appearing exine. Water leaching for 24 hours between application of the two fixatives results in severe degeneration of the exine. Thus, a reducing agent (formaldehyde) can cause exine degeneration. Formaldehyde affects only the exine, the mesine layer remaining apparently unaltered. This supports suggestions that the exine and mesine are distinct wall layers. The exine of germinating pollen seems more susceptible to formaldehyde than that of non-germinating pollen, indicating that renewed protoplasmic activity may alter the chemistry of the exine.

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