82 
Ecological Notes. 
The Transpiration of Arctic Plants. 
The first section of Dr. YVulff’s publication deals with the 
transpiration of arctic plants. Careful physiological investigations 
into the relation of plants to their environment is an essential 
factor in any attempt at a real understanding of the life of a plant- 
community, and it is Dr. Wulff's merit to have furnished us with 
the first series of such investigations on arctic plants relating to 
this particular physiological process—from an ecological point of 
view, perhaps the most important of all. On the whole, arctic 
plants belong very distinctly to the xerophiious type—they are 
usually clearly .constructed in such a way as to diminish the 
amount of water evaporated from their subaerial organs, Dr. Wulff 
used Stahl’s cobalt-paper method, and found that the time occupied 
in the reddening of the blue paper by a transpiring leaf placed 
between two pieces of the paper which had been previously dried over 
a spirit lamp, gave a good rough test of the rate of transpiration from 
the leaf-surface. Accurate quantitative estimations were of course 
quite out of the question under the conditions in which he had to 
work. The experiments were carried out on ten representative arctic 
species of flowering plants, at various hours of the day and under 
various atmospheric conditions. 
The general results showed in all cases a very feeble trans¬ 
piration compared with that which obtains under favourable 
conditions in warmer climates. One of the most sti iking and 
interesting facts brought to light was the frequent falling of the 
transpiration-rate in relatively high temperatures ( 8 . 5 - 9 . 5 °C) and 
con espondingly decreased relative humidity of the air, i.e. under 
conditions which would lead to increased transpiration in ordinary 
climates. The explanation of this phenomenon must apparently 
be sought in the supposition that the plants are, on the whole, 
adapted to transpiration at lower temperatures and with a damper 
atmosphere. They dare not make use, so to speak, of the conditions 
which favour evaporation, because their roots are unable to absorb 
enough water to cover the loss which would result. On the other 
hand, as one would expect, transpiration was very feeble when the 
air was nearly saturated, and at the lowest temperatures ( 2.5 °C). 
The most favourable conditions for transpiration appear to have 
been temperatures of about 5 °C and a relative humidity of 60 - 70 %. 
There was of course no diurnal periodicity, since the sun was 
continuously above the horizon during the whole period—several 
days—within which the observations were carried out. 
