Freshly extracted and preserved spores of Acaulospora dilatata and A. rugosa were crushed in mountants often used to assist in identifying and describing vesicular-arbuscular mycorrhizal fungi. Wall thickness increased in proportion to the amount of phenol in a mountant. Phenol also caused differential swelling of laminae so that they resembled adherent unit walls and transformed the “beaded” inner wall into a smooth membranous wall. Preservatives such as formalin, glutaraldehyde, and lactophenol obscured separation of inner unit walls, giving them the appearance of laminae in a thick, single wall. The amorphous wall type in both Acaulospora species was highly elastic in mountants of a pH less than 2.0, but was rigid at higher pH, regardless of other mountant characteristics. The amorphous wall stained dark reddish-purple in Melzer's reagent, lost iodine-staining capacity after treatment with β-amylase but not with /S-amylase, and stained orange-yellow in Dragendorffs reagent. These observations suggested that this wall was composed of quaternary ammonium compounds and polysaccharides with few exposed α-1,4 linkages. After storage of spores in preservatives, resilience and capacity of the amorphous wall to react with Melzer's reagent disappeared. Mountant and/or preservative effects on spore morphology must be known if genetic differences of taxonomic significance among spore populations are to be recognized.
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Joseph B. Morton (1986) studied this question.