40 



and yet in too scattered and irregular a manner to agree with either of the other 

 types. 



It must not be supposed that the plants thus grouped have exactly identical 

 limits ; different species show the features of the type to which they belong in 

 different degrees of intensity ; while it is obvious that these general tendencies 

 towards one side or other of the kingdom will be interfered with by the varying 

 character of soil and situation ; uniform distribution witliin the known limits of 

 their areas being prevented by some species growing only in water, bogs, or 

 marshes, or requiring for their free growth and multiplication a calcareous, sandy, 

 or other special kind of soil. 



With regard to the second mode of grouping plants, according to their 

 latitudinal or climatical range, it is obvious that the same change of climate which 

 we meet with in ascending elevated summits in more southern parts will, if we 

 proceed farther north, be found repeated at a lower and still lower altitude, till, 

 at a certain point, it will reach the sea level ; and if we connect all the points from 

 the summits of the hill on the one hand, to the coast line on the other, which are 

 characterised by the same climate, we obtain a series of zones, each of which 

 presents marked differences of vegetation. Mr. Watson considers that six is the 

 greatest number of such zones which can be satisfactorily distinguished, if regard 

 is had to the whole of Britain ; and these six range themselves into two principal 

 groups, which he terms "regions." 



In uncultivated countries, such regions and zones can be readily noted by 

 the means of the various trees, to whose growth opposing climate sets a limit. 

 In England such a method would be impracticable. The very obvious mark of 

 the limit to which cultivation can be carried is therefore adopted to distinguish 

 the boundary between these two regions ; and where, from other interfering 

 causes, culture is absent, nature supplies us with a second test in the common 

 Brake fern (Pteris aquilina), rarely absent from such spots, and whose limit 

 coincides very nearly with that of cultivation. The upper zones, separated by this 

 line of culture from the three lower ones, constitute the arctic region. Now, as 

 it is evident that no part of our county lies within this upper — the arctic region — 

 I will not dwell upon the peculiarities of its several zones, but pass at once to the 

 distingui.shing marks of those of the lower, or agrarian region. 



The diagram will show that the three zones of the arctic region are confined 

 to the mountains, the latitude of the north of Scotland not being high enough to 

 allow it to reach the coast level. The highest part of the agrarian region, com- 

 mencing on the coast line of the north of Scotland, and including, as we come 

 southward, portions of the higher hills of England and Wales, is called the 

 "super agrarian zone " ; and, as we descend from the arctic region, is marked by 

 the first appearance of the oak, the ash, hawthorn, and holly. 



Immediately below this lies the " mid agrarian zone" ; composing the coast 

 line and low grounds from the estuaries of the Clyde and Tay down to those of 

 the Dee and Humber, and a narrow belt winding round the hills of Wales. This 

 zone is chiefly characterised by the upper limit of the common maple, the dwarf 



