Corroded exines from havinga's leaf mold experiment

Abstract

Representative types of exine corrosion, based on transmission electron microscopy, are illustrated from a sample from the corrosion experiment of Havinga (1964). Exines examined came from a nylon pouch filled with a mixture of pollen, spores and sand buried in leaf mold in a greenhouse for 6 years. Deterioration was evident for most exines and had become extreme for many exines, some being corroded beyond recognition. The common denominator apparently is thinning of exines. Surprisingly, exine thinning involves loss of substance from the interior of the tectum and foot layer of the ectexine while surfaces of these layers remain intact. Early phases of thinning involve exine tunneling in rosette and other well‐defined patterns, as seen using light microscopy. These tunnels seldom actually open to the external environment. Exine thinning is accompanied by detachment of endexine. Endexines were apparently not degraded but were seen either isolated or in relatively large aggregations. Small (10–40 nm in diameter) tubules from exine substructure were recovered with very high frequency around degraded exines. Spheres outside but attached to exines are interpreted as blisters in the surface of the exine of both spores and pollen. There were no direct indications from observations made with transmission electron microscopy for microorganisms within the sites of exine deterioration. Corrosion features seen in exines from the leaf mold sample are structurally comparable with results of chemical experiments.