The Botany of Iceland - 01.12.1928, Síða 41

THE AERIAL ALGÆ OF ICELAND
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by its watér. Here there will always be a more or less considerable
amount of heat from the spring and the air will be continually fed
witli moisture from the vapours. Is is often very difficult to decide
Fig. 2. Bird-cliff on Heimaey.
wliere to draw the line hetween the thermal algæ proper and the
aerial algæ, and the same species are often found in the water and
as half desiccated incrustations on the hanks. The algal vegetation
growing on and in the often very luxuriant mosses round the springs
is of a very hydrophilous character and will hardly ever he exposed
to desiccation. The algæ growing on the siliceous sinter or on the
ground will no doubt he more exposed to desiccation, but this will
probably never he verv great. Nevertheless I include these algæ lie-
cause they grow in places where the air has free access to them