The Botany of Iceland - 01.12.1930, Blaðsíða 86

76
H.M0LHOLM HANSEN
lozenges, the surface contracting so much owing to the disappear-
ance of the water that it cracks. On the flats here described these
are of very different duration, most frequently they last a very short
time, disappearing when the surface becomes damp again. For the
vegetation these cracks, as far as I can see, are of no importance,
since it nearly always occurs on the lozenges themselves.”
In “Vegetationen paa Syd Island”, 1905, pp. 13—14, he writes,
“Open clayey flals are met with in many places.” “The vegetation
on the clayey flats is always very poor in species, and only where
the vegetation of the clayey flats is passing into the surrounding
associations do we meet wdth a greater abundance of species. The
typical clayey flats as a rule contain the same species everywhere.
The few species which are exclusively or principally found on the
ciayey ílats and must thus be designated as characteristic of them
are the following: Sedum villosum, Koenigia islandica, Spergula ar-
vensis, Juncus alpinus, J. triglumis. The most commonly occurring
are Agrostis alba, Juncus bufonius, Equiseium arvense, Epilobium pa-
lustre, Poa annua, Stellaria crassifolia, St. media, Ceraslium vulgare,
Polygonum aviculare, Sagina procumbens. More rarely we meet with
Triglochin palustre, Alopecurus fulvus, Scirpus pauciflorus, Eriophorum
Scheuchzeri, Sedum annuum, Poa glauca, Rumex acetosa, Silene ma-
ritima, Phleum alpinum, Mgosotis arvensis, Veronica serpgllifolia,
Rnmex acetosella, Thgmus serpgllum, Leontodon.”
By the above quotations from H. Jónsson’s descriptions of the
vegetation and by the circling results given here the flag vegetation
has been characterised floristically. If we are to characterise the
vegetation biologically, the best way will be to compare the bio-
logical spectra of the flag and the neighbouring vegetations, i. e. tlie
mo and the jaðar. Table 18 gives the biological spectra of these
types of vegetation at Björk and Lækjamót, viz. respectively moist
mo, flag (or flag mo), jaðar (or mýri).
It will appear from tlie table that the flag vegetation is poorer
in species and shows less density of species than the surrounding
types of vegetation, the mo and the jaðar. This applies especially
to the Koenigia flag. As regards the content of Raunkiær’s life
forms, the flag is especiallj' remarkable by its high Th percentage.
As shown above, the Subularia flag had a Th percentage of 71, the
Koenigia flag a Th percenlage of 20.9, and the flag mo a Th per-
centage of 9.4. The table likewise shows a comparatively high H
percentage and comparatively low Ch and G percentages. The pro-