. Lichens. Lichens. LICHEN COMMUNITIES 379 indifferently on any kind of shore rock either siliceous or calcareous. Wheldon and Wilson^ noted this indifference to substratum on the Arran shores, where a few calcicolous species such as Verrucaria nigrescens, V. maculiformis, Placodium tegularis and PI. lobulatum, grow by the sea on siliceous rocks. They suggest that the spray-washed habitat affords the conditions, which, in other places, are furnished by limestone. The greater or less proximity of the salt water induces in lichens, as in other maritime plants, a distribution into belts or zones
. Lichens. Lichens. LICHEN COMMUNITIES 379 indifferently on any kind of shore rock either siliceous or calcareous. Wheldon and Wilson^ noted this indifference to substratum on the Arran shores, where a few calcicolous species such as Verrucaria nigrescens, V. maculiformis, Placodium tegularis and PI. lobulatum, grow by the sea on siliceous rocks. They suggest that the spray-washed habitat affords the conditions, which, in other places, are furnished by limestone. The greater or less proximity of the salt water induces in lichens, as in other maritime plants, a distribution into belts or zones which recede gradually or abruptly according to the slope of the shore and the reach of the tide. Weddell^ on the Isle d'Yeu delimited three such zones: (i) marine, those nearest the sea and immersed for a longer or shorter period at each tide; (2) semi-marine, not immersed but subject to the direct action of the waves, and (3) maritime or littoral, the area beyond the reach of the waves but within the influence of sea-spray. In the course of his work he indicates the lichens of each Fig. 122. Ramalina siliqtiosa A. L. Sm. Upper zone of barren plants (after M. C. Knowles, R. Welch, Photo.]. In Ireland, a thorough examination has been made of a rocky coast at Howth near Dublin by M. C. Knowlesl She recognizes five distinct belts ^ Wheldon and Wilson 1913. 2 Weddell 1875. ' Knowles 1913.^. 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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