LIMNOLOGICAL PKOBLEMS 
387 
beds of vegetation are able to collect considerable amounts of warmth 
is well known through Kerner's investigations, and the phenomenon 
has been described later by Brinkmann (1905, p. 27). Neither of 
these seems to know that the enormously high temperatures (30° C.) 
occurring in the upper layers of the vegetation are very distinctly 
limited to the surface ; at about 1 m. below the surface the tempera- 
ture is often only 15-18° C. Thrusting an arm down through such a 
Sphagnum-bed warmed by the sun, we get an intense feeling of cold 
in the tips of the fingers and a feeling of great warmth up at the 
shoulders. I believe that the great warmth which thus arises in the 
littoral region is carried by the waves, especially on days when the 
wind rises before cooling begins, out over the lake, and is of benefit 
to the surface of the lake. To demonstrate further the importance 
of the littoral zone as a warmth-producing factor, I give here some 
observations from recent years. 
On 3rd March 1907, when Fureso was everywhere covered with 
about 12 cm. of ice, the temperature towards the shore in about 
6 cm. of water about f m. from the margin of the ice was not less 
than 7° C. (sheltered thermometer) ; bright sunshine, time from 
noon to 4 p.m. The air temperature in the shade was -|-0°*5 C. ; 
at 5 p.m. the temperature of the water at the same place had 
gone down to +1°"5, the air temperature to — 0°"5. Shortly after 
the free margin of water had certainly become coated with a thin 
layer of ice. 
On 28th March 1907, when the temperature of the air in the shade 
at 2 p.m. was about 10° C, the temperature of the surface-water in 
Esromso in the pelagic region was 2° '5. On the north coast of 
Noddeboholt, close to the shore, exposed to the land wind from 
N.N.W., the temperature of the water was 5°'l ; but on the south 
side, on the borders of the vegetation, in bright sunshine, 17°'2 ; in 
the ground only about I m. from the water's edge, 7° "2 C. At the 
same time numerous bog-hollows in Grib forest were still covered 
with ice. In a Sphagnum-moss which was strongly lighted by the 
sun, and whose sides were completely frozen and hard as stone, the 
thermometer a few cm. below the surface of the Sphagnum-bed 
registered 12° C. 
On 12th April 1906 one of the experimental ponds belonging to 
the Fresh- water Biological Laboratory was still covered with ice on 
the sheltered side and the margin frozen ; on the opposite, sunny side 
the temperature was 7° C. On 29th March 1907 all three experimental 
ponds were on the sheltered side, which at this time of year never 
has any sunlight, covered by 6 cm. of ice. The temperature of the 
air in the shade was 11° C. at 2 p.m. The temperature of the water 
on the sunny side of the ponds, amongst the vegetation, was 14-17° C. ; 
