II. ASCENDING ZONES. Q1 
II. Arctic Region. 
6. Super-arctic zone—Salix herbacea, without Calluna. 
. Mid-aretic zone—Calluna vulgaris, without Erica. 
. Infer-arctic zone—Erica Tetralix, without Pteris. 
eo 
I. Agrarian Region. 
3. Super-agrarian zone—Pteris aquilina, without Rhamnus, &e. 
. Mid-agrarian zone—Rhammnus catharticus, without Clematis. 
1, Infer-agrarian zone—Clematis, Rubia, Cyperus longus. 
~w 
“Unless the highest part of Snowdon can be deemed to attain 
the super-arctic zone, none of the before-explained provinces will 
include the full series of six zones. Elsewhere the hills are not 
sufficiently lofty to pass the mid-arctic zone, until we arrive at the 
Highland provinces, all three of which have their highest summits 
clearly above the limits of the Calluna; but the lowest portions of 
these provinces, near their coast-line and southern boundary, fall 
barely within the mid-agrarian zone.” 
“It is probable that six such zones are quite as many as can be 
satisfactorily distinguished when attention must be directed to the 
whole surface of Britain. Even with six only, it would be useless 
to attempt very great precision in assigning the species to their 
respective zones. We must disregard the occasional and slight. 
trespass of a species into a zone above or beneath those to which 
it is otherwise restricted by its natural adaptation to their climate. 
Such trespasses (if the expression be allowable) are usually found 
in connexion with some local peculiarity by which the true climate 
is varied, or its influence on the plants modified. For example, 
the cool spray of a waterfall, or the efflux of a cold spring, will 
support the species of a colder climate than is natural to the 
latitude and elevation. And, on the contrary, the plants of a 
warmer climate will grow on the south face of rocks which are 
raised above the altitude where the same species cease to exist in 
more bleak situations. These apparent exceptions come incon- 
veniently in the way of precise lines on botanico-geographical 
maps. Thouyh such lines muy be made to look very clear and 
