The Botany of Iceland - 01.12.1945, Blaðsíða 137

THE VEGETATION OF CENTRAL ICELAND
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/^s-o/z/e S /‘ro/'//e C
Fig. 16. Flá on Háumýrar (Tab. XXV,3). Profile A was taken
along the dotted line. 1, Lake; 2, Eriophorum polystachyum-Assoc.,
Be!t 1 ; 3, Carex rigida—C. rariflora-Assoc., Belt 2 ; 4, Salix-Assoc.,
3 í 5> Salix—Elyna-Assoc. Open vegetation, Belt 4.
Profile B, a moderately high rúst; Profile C, a low rúst. The
figures indicate the same as in Profile A.—Note the missing belts.
Cetraria or Alectoria growths are found on the tops of the rústs that
the formation strongly approaches the Scandinavian lichen heath.
There is one more feature which characterises the flá. The rústs,
at any rate the largest of them, contain a nucleus of ice throughout
the greater part of or the whole summer. Hannesson (1928, p.
141) says (translated from the Icelandic) : “The ice persists in the
rústs the whole summer, but between them it is absent by midsummer.
Under all the rústs examined by me an ice socle was found, which
rested on the solid gravel flat.” Nielsen (1933) is of the same
opinion. I have no reason to doubt the contention of these two eminent
investigators. Personally I have only observed this phenomenon quite
superficially. In the suramer of 1933, which was especially warm, I
tried to ascertain ice in some rústs by means of a walking-stick c. 80 cm
long, but did not succeed in touching any ice nucleus; however, this
does not exclude that the nucleus may have occurred at a greater
depth. It is worth, also, to bear in mind that the heat of this summer
far exceeded the normal. In the summers of 1935 and 1937 I in-
vestigated some rústs in the same way and then found ice at a depth
of 40-50 cm. All the investigations were made about the same time,
between July 20th and August ist. This, it is true, does not prevent