. Lichens. Lichens. .V-g-"- i^' Fig. 56. Dermatocarpon miniatum Th. Fr. (S. H., Pholo.). both cortices consist of a compact many-layered plectenchyma. The same structure occurs in Umbilicaria pustulata and in some species of Gyrophora, which, having only a single central hold-fast, gain the necessary stiffening through the increase of the cortical layers. In the Stictaceae there are a large number of widely-expanded forms, and as the attachment depends mostly on a somewhat short tomentum, strength is obtained here also by. the thick plectenchymatous cortex of both surfaces. When areas
. Lichens. Lichens. .V-g-"- i^' Fig. 56. Dermatocarpon miniatum Th. Fr. (S. H., Pholo.). both cortices consist of a compact many-layered plectenchyma. The same structure occurs in Umbilicaria pustulata and in some species of Gyrophora, which, having only a single central hold-fast, gain the necessary stiffening through the increase of the cortical layers. In the Stictaceae there are a large number of widely-expanded forms, and as the attachment depends mostly on a somewhat short tomentum, strength is obtained here also by. the thick plectenchymatous cortex of both surfaces. When areas denuded of tomentum and cortex occur, as in Lobaria pulmonaria, the under surface is not sensibly weakened, since the cortical tissue remains connected in a stout and firm reticulation. b. By development of Veins or Nerves. Certain ground lichens belonging to the Peltigeraceae have a wide spreading thallus often with very large lobes. The upper cortex is a many-layered plectenchyma, but the under surface is covered only by a loose felt of hyphae which branch out into a more or less dense tomentum. As the firm upper cortex continues to increase by intercalary growth from the branching upwards of hyphae from the meristematic gonidial zone, there occurs an extension of the upper. 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 resemble the original Smith, Annie Lorrain. Cambridge, At the University Press
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