The Botany of Iceland - 01.12.1912, Blaðsíða 140

126
H. JÓNSSON
small pools, often forms a continuous fringe, the upper branches
either reaching to or lying on the surface of tlie water. In such
pools Chœtomorpha tortuosa sometimes occurs in fair abundance
loose upon the surface of the water; its íilaments are usually densely
matted together.
Fucus inflatus f. linearis grows even more socially. At times it
is almost tlie dominant species in the smaller pools, although, ralher
frequently, several other species are found intermingled with it.
Tliis form is a biological variety of Fucus inflatus which, in the
pools, exists evidently under less favourable circumstances; lliis is
one cause of its small size and feeble structure, although anotlier
is that it is not exposed, to any extent worthy of mention, to the
beat of the waves. Rosenvinge has especially shown this to be
the case as regards Greenland. Rosenvinge explains the frequent
occurrence of tliis form in the pools by the fact that the eggs of
F. inflatus are carried into the water-filled depressions by the move-
ment of the water and accumulate there. This explanation is un-
doubtedly correct, and, as Rosenvinge points out, all intermediate
stages between the feeble pool-form and tlie typical form can be
demonstrated. To any one who has seen this endless variation in
nature, it seems so certain tliat it is due to the influence of outside
factors, that experimental proof is almost superlluous.
The uppermost pools are generally extremely poor in species;
and, besides those already mentioned, only Enteromorpha inlestinalis
occurs in any great abundance. Wliere the coast is exposed, the
uppermost pools may, however, have a resemblance to the lower
ones of the upper littoral zone — a natural consequence of the
exposure. On more exposed parts of the coast a fringe of small
Monostroma Grevillei is often found, almost on the surface of the
water itself. At one place in E. Iceland I took the temperature of
such a submerged plant-covering, and the thermometer showed
20° C. (June 13). The vegetation was also somewhat injured, and
evidently did not prosper under these conditions.
High up on a rocky coast to the south of Vattarnes in E. Ice-
land, I came across a pool-vegetation. I did not measure the alti-
tude of the spot, but I do not think that I was greatly mistaken
in estimating it at 70—100 feet above sea-level. As regards the place,
I noted in my dairy — “High rocky coast, land-plants grew round
the alga-pools. The water in the pools must be replenished with
rain and heavy surf, which soinetimes fail for long periods during