Fig. 122. Ramalina siliquosa 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. Knowles[1187]. She recognizes five distinct belts beginning with those furthest from the shore though within the influence of the salt water:

(1) The Ramalina belt. In this belt there are two zones of lichen vegetation: those in the upper zone consist mainly of barren plants of Ramalina siliquosa[1188], rather dark or glaucous in colour with much branched fronds which are incurved at the tips ([Fig. 122]). They are beyond the direct action of the waves. The lower zone consists also mainly of the same Ramalina, the plants bearing straight, stiff, simple, or slightly branched fertile fronds of a pale-green or straw colour ([Fig. 123]). The pale colour may be partly due to frequent splashings by sea-spray.

Ramalina siliquosum in both zones takes several distinct forms, according to exposure to light, wind or spray, the effects of which are most marked in the upper zone. The plants growing above the ordinary spray zone generally form sward-like growths ([Fig. 124]); at the higher levels the sward growth is replaced by isolated tufts with a smaller more amorphous thallus which passes into a very small stunted condition. The latter form alone has gained and retained a footing on the steep faces of the hard and close-grained quartzite rocks. “On the western faces, indeed, it is the only visible vegetation.” The dwarfed tufts with lacerated fronds measuring from 1/4 to 1/2 an inch in height are dotted all over the quartzites. On the sea faces the plants are larger, but everywhere they are closely appressed to the rock surface. At lower levels the fronds lengthen to more normal dimensions. “On these steep rock-faces there is a complete absence of any of the crustaceous species. The problem, therefore, as to how the Ramalina has obtained a foothold on these very hard precipitous rocks, which are too inhospitable even for crustaceous species is an interesting and puzzling one.”

In the Ramalina zone along with the dominant species there occur occasional tufts of R. Curnowii and R. subfarinacea, the latter more especially in shady and rather moist situations. There are also numerous foliaceous and crustaceous lichens mingling with the Ramalina vegetation ([Fig. 125]), several Parmelias, Physcia aquila, Xanthoria parietina, Buellia canescens, B. ryssolea, Lecanora atra, L. sordida, Rhizocarpon geographicum and others. In the main these are arranged in the following order descending towards the sea: