TEN YEARS' PROGRESS IN LICHENOLOGY. 277
etc. Her observations do not always coincide exactly with those
of Cotton and Knowles, especially as stated in the paragraphs
describing the Lichina zone.
A detailed description of lichens as they occur on a steep
rocky coast was published in a paper by M. C. Knowles (4b).
Before the publication of the results of her investigations, in
1913, very little detailed work on this aspect of lichen growth
had been attempted anywhere. The author vividly describes
the general appearance of lichen belts in these words "As one
walks along the tops of the headlands when the tide is low, a
dark band, which seems like a stain on the rock-surface, can be
distinctly traced upon the cliff faces and on the rocks of the sea
shore. At high spring-tide the band is almost hidden by the
water, but it becomes wider as the tide falls; and at low spring
tide it seems to end, on the cliffs and high rocks, in a well-defined
line running parallel to the surface of the sea at a few feet below
the level of ordinary high tide, contrasting in a striking manner
with the paler band of the barnacle-covered rocks below it."
Three almost unbroken colour belts occur on the Howth
coast. They are described as the black, the orange, and the
light grey-green belts. The black belt is further divided into
two zones, the lower being the zone of marine lichens, first de-
scribed by M. C. Knowles ; it consists of Verrucaria microspora,
V. striatula and V. mucosa. The upper is the Verrucaria maura
zone, which is bordered by a fringe of Lichina pygmaea below and
by L. confinis above.
The orange belt is formed mostly of bright orange-coloured
lichens as Xanthoria parietina, Placodium murorum, and P.
decipiens, var. lobulatum.
Above the orange is a wide grey-green belt of Ramalina
siliquosa, a lichen which is abundant on rocky coasts, especially
in the west of England, its mass of colour being a striking
feature of several localities.
Both the Clare Island Report and the paper on Howth
Head direct attention to the differences between the
lichen growth on silicious and on calcareous rocks. Such dif-
ferences are often plainly evident, but from this fact it cannot
be inferred that the composition of the rock is always the main
factor in determining the presence of the lichen upon them.
In "Lichens of Arran" (5a) the reader is reminded that certain