The Botany of Iceland - 01.12.1912, Blaðsíða 122

108
H. JÓNSSON
appears to have extended too high upwards, and where, when the
weather is calm, it is not wetted daily by the sea at and about
neap-tide. On a warm summer’s day Pelvetia can become so dry
in such places that, when gathered, it needs no furtlier drying —
the same may also be the case with Fucus spiralis. The individuals
of Pelvetia whicli grow at that. height, i. e. sometimes right up in
the Verrucaria maífra-belt, are usually very small (about 2 cm. in
height) and occur closely pressed to the rock; then they are often
Fig. 3. Pelvetia canaliculata abovc, Fucus spiralis below. Illustration of a typical Pelvetia-
Fucus-spiralis-community. Reykjavík, Aug. 13, 1909. (From phot. by Hesselbo.)
found especially in crevices, and the new fronds may bear a sur-
prisingly close resemblance to a rosette. Lower down, where the
vegetation is luxuriant, the plants are about 8 cm. in height. Pelvetia
is the smallest of the Fucaceœ on these coasts; it differs from the
others not only by its small size, but also by its ligliter, yellowish-
brown colour, and its channelled frond, etc. The cliannelled frond
must be useful to a plant which is so exposed to the desiccating
action of the air as is the case with Pelvetia, because, by reason of
their being rolled, the under-side of the fronds is less exposed to
wind and weather.
It is characteristic of the zonal division of the Fucaceœ on the