. Bulletin of the British Museum (Natural History) Botany. 236. Fig. 4 Cortical structure of the Thelotremataceae viewed with the scanning electron microscope, (a) Splitting cortex and aculeate hyphae of Myriotrema glaucophaenum (Hale 47 062). (b) Exfoliating sheet of Ocellularia emersa (Hale 51 068). (c) Internally splitting cortex of Myriotrema fluorescens (Hale 47 152). (d) Internally splitting cortex of Ocellularia croceopora (Hale 46 186) showing incorporation of sheets into the medulla. marivelensis, O. massalongoi, O. papillata, O. pluripora, O. polillensis, O. rassagala, O. subsimilis,
. Bulletin of the British Museum (Natural History) Botany. 236. Fig. 4 Cortical structure of the Thelotremataceae viewed with the scanning electron microscope, (a) Splitting cortex and aculeate hyphae of Myriotrema glaucophaenum (Hale 47 062). (b) Exfoliating sheet of Ocellularia emersa (Hale 51 068). (c) Internally splitting cortex of Myriotrema fluorescens (Hale 47 152). (d) Internally splitting cortex of Ocellularia croceopora (Hale 46 186) showing incorporation of sheets into the medulla. marivelensis, O. massalongoi, O. papillata, O. pluripora, O. polillensis, O. rassagala, O. subsimilis, Thelotrema magnificum, T. piluliferum, and T. platysporum). Exfoliation of the cortex was probably first observed by Miiller Argoviensis when he described Anthracothecium (Myriotrema) desquamans as having 'plaguliformi desquamans'. Using a light microscope one can see the cortex splitting into thin sheets which may curl up and peel off the surface (Fig. lb). The cortex may also split internally, giving rise in extreme cases to alternating, stratified layers of cortex and medulla, as in Ocellularia croceopora (Fig. 4d). These layers may be only one cell layer thick or 20 pm or more, regenerating from below as sheets subdivide or peel off. The constant occurrence of aculeate hyphae in species with an exfoliating cortex suggests that these hyphae initiate or promote the splitting process in some way since they can be seen on the surface of newly exfoliating sheets (Fig. 4b). The same phenomenon occurs in the Graphidaceae (Wirth & Hale, 1978) and will surely be discovered in other crustose groups. There is a high degree of correlation between cortical structure and chemistry, although I have not tested this statistically. Species with hypoprotecetraric acid or no substances appear. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemb
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