Iowa County democrat. [volume] (Mineral Point, Wis.) 1877-1938, 1901-09-05

ARCTIC VEGETATION.
Light Compensates For Inadequate
Warmth.


Warmth.
Prof. j. Wicsncr Of Vienna univeY-
sty, who for some years has been
engaged in researches on the require
ments Of plants in the matter of
light, has come to the following con.
cusions with regard to the plants
Of the Arctic regions. The demonstra-
ton previously put forward by him
with regard to low and middle
attitudes, that with the increase ell
latitude the light requirement OIL
plants also rises, has been shown by
observations made in Norway and at
Advent bay, Spitzborgon, 1912 north
latitude, to apply equally to sub-arctic
and Arctic regions. The reasons Tor
this marked need of light are the low
temperatures which prevail at the
yegCtativc period, the want Of heat
the amount of which must therefore
increase with the decrease Of tenn
pcraturc. 1t thus comes about that
limit is set to the migration toward
the pole of bush and tree vegetation
less by the cold of winter than by the
contantly increasing need Of light
which can Of course, be less and less
satisfied. As a rule, the plants Of the
far north can stand hut small
dminution Of their quaHtum Of light
such as Is caused by tho interrogation
Of the suns rays through the con
liguration of the country,
DR.. Pouckor's researches on noun
tain shadow have shown how the
amount Of light required can be laid
down with precision in each particular
case The intensity Of the direct sun
light to which Arctic plants are eX
posed is very slight, for 1t only be
comes perceptiblo when the sun
reaches an altitude of % degrees
above the horizon, whereas in the
most favorable case on June q, the
sun only attains, at Advent bay, an
altitude Of 80 to 35 degrees. Direct
sunlight here at best reaches the
strength of the light radiatcd from
the whole cXpanse Of the Sky, tho so
called "diffuscd light" SO that the
whole illumination available for polar
plants is at most double the amount
Of the difrusod light. The high A, ne
plants of mean ATTITUDES, on the con
trary, enjoy an amount of illumination
which may be estimated at a max
imum of at least four times that due
to the diffused light, the sun reaching
a midday altitude in summer of 66 to.
90 degrees These differences result
ns BONNER has shown, in considerable
variations in the organs Of plants 81
like species, which occur both in high
Alpine and high Arctic regions In
middle ATTITUDES the effect Of aspect
on vegetation is very striking, the
northern slopes OF mountains being
often bare Of plants. But In view OF
the much nearer approach to a com
plete circuit round the horizon made
by the sun in Arctic ATTITUDES it Is
easily seen that this influence is less
felt there than anywhere.
Of much interest, lastly, is the de-
monstration Of the influence exercised
by dircrential lighting on the form cf
trees, the low anglo Mt which light is
received especially favoring the
ryramidal shape in Arctic attitudes,
though this is by no means deterimen-
tai under the moro nearly vertical
lighting of low attitudes. The cyp-
ressos of the south are, in fact pro-
tectod by their form from the in
| furious effects OF vertical sun, while
the same form enables tho frs, pines
and white poplars of Norway and
Sweden to make tho most of the
horizontal rays of tho northern sun.
British Geographical Journal.