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Dissolution of Weddellite, Calcium Oxalate Dihydrate, in Pyxine Subcinerea

Published online by Cambridge University Press:  28 March 2007

P. Modenesi
Affiliation:
Dipartimento per lo Studio del Territorioe delle sue Risorse, Sede di Botanica, Corso Dogali 1/m, 16136 Genoa, Italy.
V. Bombardi
Affiliation:
Dipartimento per lo Studio del Territorioe delle sue Risorse, Sede di Botanica, Corso Dogali 1/m, 16136 Genoa, Italy.
P. Giordani
Affiliation:
Dipartimento per lo Studio del Territorioe delle sue Risorse, Sede di Botanica, Corso Dogali 1/m, 16136 Genoa, Italy.
G. Brunialti
Affiliation:
Dipartimento per lo Studio del Territorioe delle sue Risorse, Sede di Botanica, Corso Dogali 1/m, 16136 Genoa, Italy.
A. Corallo
Affiliation:
Dipartimento per lo Studio del Territorioe delle sue Risorse, Sede di Botanica, Corso Dogali 1/m, 16136 Genoa, Italy.

Abstract

On the thalline lobes of Pyxine subdnerea there are delimited patches of pruina consisting of bipyramidal prisms, bipyramids and druses of weddellite, i.e. calcium oxalate dehydrate (COD), as revealed by X-ray analysis and SEM observations. The disappearance of the crystals from older thalline areas is preceded by an increase in the frequency of corrosion figures, in the form of etch square pits, and a decrease in the number of crystals occurring on the thalline surface. These features follow a dissolution gradient from the lobe apex towards the proximal edges of the patches. The corrosion figures are linked to the thermodynamic metastability of COD. Partial dissolution of the crystals, performed in water and in EDTA, has confirmed this latter assumption. It is thought that the disappearance of pruina, which interferes with the transmission of light to the algal layer, may allow the formation of soredia in mature thalline portions.

Type
Research Article
Copyright
Copyright © British Lichen Society 2001

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