104 FORESTRY OF NORWAY. 
lost. From this it may be inferred that unless what 
has been thus withdrawn, or its equivalent, be restored by 
the decomposition of rocks allowed to go on while the 
land lies fallow or is utilised by the culture of some 
other kind of crop, or by a supply of it in manure, the 
soil will sooner or later become exhausted of these constitu- 
ents ; and observation has shown that then the land will 
no longer yield that crop.., So is it with land altogether 
devoid of constituents required in the production of the 
same or. other vegetables. And thus is the geographical 
distribution of trees, and of arborescent as well as of herba- 
ceous plants, to a great extent determined: 
It may be instructive to bear in mind that what is 
required for the growth and reproduction of a plant, the 
seed of which has found its way to any spot, is not only 
heat and moisture, but these in quantity, defined within 
a limited range, varying in many cases with the successive 
stages of germination, growth, flowering, ripening of the 
fruit, and the casting of the seed, a departure from which 
at any one of these stages, or at some stages intermediate 
between them, imperilling the result. But not less essen- 
tial and necessary to the continued growth of the plant is 
a soil supplying in appropriate form and in appropriate 
quantities the nutriment required by the plant. 
‘The beautiful indigenous plant, the “lady's slipper,” 
grows, says Schleiden, ‘over all parts of the Swiss Fore 
Alps, where the soil is formed of the Alpine limestone; 
it accompanies the whole Swabian musselkalk, and dis- 
appears suddenly when we come to the sand of the Jura 
and keuper formations on this side of the Danube. It 
‘next makes its appearance on the musselkalk of Turin- 
gia, and comes down with that on the Werr as far as the 
neighbourhood of Gotlengen, and it leaps over the 
Bunter sandstone of the lower Hichsfeld, and the gran ‘te o 
the Upper Hartz, and it again gladdens the eye «. the 
wanderer on the calcareous formations eastward of the 
Brocken. 
