The Botany of Iceland - 01.12.1912, Page 106

92
H. JÓNSSON
zone and the belt of Laminaria in the sublittoral zone. This is
possibly the reason why the semi-littoral zone is richest in species.
In Table 7, 64 species are recorded as sublittoral. Besides
these, semi-littoral species occur in this zone, especially as epiphytes,
or, rnore rarely, as undergrowth. 12 species, almost all semi-littoral,
which extend to a greater depth than 10 metres are mentioned in
the table. In addition, about 14 species can be regarded as epi-
phvtic, particularly in the upper part of the sublittoral zone. The
sublittoral vegetation is thus composed of 64 sublittoral species and
of about 26 semi-littoral species, or about 90 species in all.
Lower Limits of Growth.
As far as the lower limit of growth is concerned the species
which are found below low-tide must be dealt with collectively.
In the following table, which shows the lower limits of growth, all
the depths at which species have been known to occur have been,
as a rule, taken into consideration, and thus the table does not
indicate the depth of their general distribution or the depth at
wliich they form associations (see under Vegetation). In the table,
2 red algæ are omitted, as I have no further knowledge regarding
their habitats (31, pp. 140, 141). These species are Delesseria Baerii and
Bonnemaisonia asparagoides. As regards the green algæ it must also
be stated that I have not taken into consideration the records from
greater depths than 10 metres. I myself am responsible for some
of these records; the algæ often were detached, but sometimes it
appeared as if they really had been growing at the depth recorded.
I always, however, have entertained some doubt concerning this,
and consequently prefer at present not to consider records from
such depths. Regarding Chlorochgtrium inclusum the record is cor-
rect, as it grew in Turnerella, which was attached to the bottom
at a depth of 30 metres. For Gomontia and Ostreohium I have given
the most common depth, down to about 40 inetres, but I have also
obtained these species, growing inside an old shell of Mga, from a
depth of about 60 metres.
It should be further stated that I do not know the depth to
be given for Desmarestia ligulata. This species has been found by
Ove Paulsen between the Vestmannaeyjar and South-Iceland; I
presume that it grew at a depth of about 20 metres.