Variations in fungal spore dimensions in relation to preparatory techniques for light microscopy and scanning electron microscopy

SUMMARY The volumes of urediospores of Uromyces viciae‐fabae and ascospores of Sordaria humana in the critical point‐dried, freeze‐dried, osmium vapour‐fixed/freeze‐dried, frozen‐hydrated and ‘wet’ states were measured. Dried spores shrank and were significantly smaller than frozenhydrated and ‘wet’ spores. Urediospores exhibited a greater range of dimensional changes in relation to the preparatory treatment than did ascospores. Ascospores, dried in different ways, were not significantly different from each other but were significantly smaller than frozenhydrated ones. Both urediospores and ascospores dehydrate naturally and collapse. On wetting they imbibe water rapidly and swell. Low temperature scanning electron microscopy may be suitable for investigating fungal spores in their ‘natural states' on the leaf surface.