Structural stabilization for electron microscopy of pollen from herbarium specimens

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Abstract
The rehydration of dried pollen and spores is a common technique to obtain information on nuclear condition, cytoplasmic storage materials, the intine and other aspects of pollen morphology when fresh material is unavailable. Pollen grains are rehydrated and consequently expanded by most aqueous solutions although electron microscopical examination will reveal considerable variation both in stainability and quality of expansion following embedding. That variation, we suggest, is due to substances extracted during hydration and processing. Rehydration of herbarium material with aldehyde solutions containing cations known to stabilize mucosubstances has greatly improved staining and recovery of shape equivalent to fresh pollen of Nymphoides and Menyanthes (Menyanthaceae). It is our contention that rehydration of dry pollen with attention to the stabilization of mucopolysaccharides substantially increases the information available from herbarium material and should supplement KOH and acetolyzed specimens.