Evening star., 1901-09-21
ARCTIC VEGETATION.
Requirements of Plant Life in thu
Matter of Light.

Matter of Light.
From the British Geographical Journal.
Prof j. Wiesner Of Vienna University
who for some years has been engaged in
researches on the requirements of plants
in the matter Of light has come to the fol-
lowing conclusions with regard to the
plants Of the arctic regions. The demon
stration previously put forward by him
with regard to low and middle latitudes,
that with the increase Of latitude the
light requirement of plants also rises, has
been shown, by observations made in Nor
way and at Advent bay, Spitzenbergen,
1912 north latitude, to apply equally to
subarctIc and arctic regions. The reasons
for this marked need of light are the low
temperatures which prevail at the vegeta-
tive period, the want of heat being made
up for by excess Of light, the amount of
which must therefore increase with the
decrease Of temperature. It thus comes
about that limit is set to the migration
toward the pole of bush and tree vegeta-
tion less by the cold Of winter than by the
conStantly-increasing need Of light, which
can, of course, be less and less satisfied.
AS a rule, the plants Of the far north can
stand but a small diminution of their guam
tum Of light, usch as is caused by the in
Perception Of the suns rays through the
configuration of the country.
DR.. Peuckers researches on mountain
light required can be laid down with pre-
cision in each particular case. The inten-
sity of the direct sunlight to which arctic
plants are exposed is very slight for 1t
only becomes perceptible when the sun
reaches an altitude Of 10 degrees above the
horizon, whereas In the most favorable
case. on June 21, the sun only atttains, at
Advent bay, an altitude of 80 to 35 degrees.
Direct sunlight here at best reaches the
strength Of the light radiated from the
whole expanse of the sky, the so-called
"diffused light" so that the whole illumi-
double the amount Of the diffused light.
The high Alpine plants of mean 1atitudes,
on the contrary, enjoy an amount of illumi-
nation which may be estimated at maxi
mum Of at least four times that due to the
diffused light, the sun reaching a midday
altitude in summer Of 66 to 60 degrees
These differences result, as BONNER has
shown, in considerable variations in the
organs of plants of like Species which oc-
cur both in high alpine and high arctic
regions. In middle latitudes 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 complete circuit
round the horizon made by the sun in arc
tic latitudes, 1t is easily seen that this
influence is less felt there than anywhere.
OF much interest, lastly, Is the demon
Stration of the influence exercised by diff
ferential lighting on the form Of trees the
low angle at which light is received es-
peclally favor1ng the pyramidal shape In
arctic latitudes, though this is by no means
detrimental under the more nearly vertical
lighting Of low latitudes. The expresses
or the south are, in fact, protected by their
form from the injurious effects of a yer-
tlcal sun, while the same form enables the
hrs, pines and white polars Of Norway and
Sweden to make the most Of the horizontal
rays of the northern sun