1 879.] 
The Action of Light on Plants. 
787 
The term light is here used to express all those rays of 
he spedtrum which are visible to a perfedtly-formed human 
eye ; by actinic principle is meant the principle to which the 
phenomenon of chemical change under solar influence be- 
longs ; and by calorific radiations , not merely those effedts 
which are traceable by any thermometric instruments, but 
also those which we can detedt by the protedtion from 
change produced by a class of rays existing near the point 
of maximum heat in the spedtrum. In the spring, when 
seeds germinate and young vegetation awakes for the repose 
of winter, we find an excess of that principle which imparts 
the required stimulus ; in the summer this exciting agent 
is counterbalanced by another possessing different powers, 
upon the exercise of which the strudtural formation of the 
plant depends ; and in the autumnal season these are 
checked by a mysterious agency, which we can scarcely 
recognise as heat, although connedted with thermic mani- 
festations upon which appears to depend the development 
of the flower and the perfection of the seed.” 
The phenomena which the prolonged action of sunlight 
produces on vegetation in high latitudes are recorded by 
M. J. A. Broch, in a work recently published.* 
The farther we go eastward from the Gulf Stream the 
more severe is the climate, even though the degree of lati- 
tude be the same. Thus Scandinavia and Finland possess 
an exceptionally mild climate, considering their high polar 
altitude. Indeed barley and oats will ripen in the most 
northern distridts of Norway, Sweden, and Finland, and 
immense forests are met with ; whilst in Iceland, Green- 
land, and the Polar confines of Russia and America, the 
earth is bare and sterile, and there are eternal snows. The 
cause of these advantageous climatic conditions is to be 
attributed to the enormous mass of warm water and hot 
air which the Gulf Stream brings down from the Equatorial 
region to the coast of Norway, which coast it approaches 
between 6o° and 6i° of latitude. This circumstance, to- 
gether with the difference in the geological formation of the 
various northern countries of Europe, naturally lead to 
certain dissimilarities in the respedtive climates of these 
countries. Comparing Norway and Sweden, for instance, 
in the former the sun is moist, cloudy, and the 
quantity of rain considerable, the winters mild and the 
summer cold ; while in Sweden the sun is brighter, the 
* Le Royaume de Norvege et le Peuple Norvegien, par J. A. Broch, Ancien 
Ministre de Norvege. 
