INTRODUCTION. 9 
so conspicuous a position, so now in the annals of 
physical geography they are entitled to a promi- 
nent place. With the exception of the grasses— 
Nature’s special favourites—they are the most 
abundant of all plants, possessing inconceivable 
myriads of individual representatives in every part 
of the globe, from which unfavourable conditions 
exclude all other vegetation. And thus they con- 
tribute, far more than we are apt from a superficial 
observation to imagine, to the picturesque and 
romantic appearances exhibited by scenery, and to 
the formation of that richly woven and beautifully 
decorated robe of vegetation which conceals the 
ghastly skeleton of the earth, and hides from our 
view the rugged outlines and primitive features of 
nature. They are the first objects that clothe the 
naked rocks which rise above the surface of the 
ocean ; and they are the last traces of vegetation 
which disappear under degrees of heat and cold 
fatal to all life. Their structure is so singularly 
varied and plastic, that they are adapted to every 
possible situation. In every country they form an 
important element in.the number of plants, the 
proportion to flowering plants decreasing from and 
increasing towards the poles. Taking them as a 
whole, and in regard to their size, they occupy a 
larger area of the earth’s surface than any other 
kind of vegetation. There are immense forests of 
