4 THE STORY OF PLANT LIFE 
None the less at the top of Ben Lawers and 
similar mountains in Scotland arctic alpine plants 
grow, and there is a typical vegetation of Saxifrages 
and kindred plants. Up to the altitude of rooo ft., 
moreover, wheat and other crops will grow, and this 
zone of cultivation marks the limit of certain plants 
that also cannot exist at higher altitudes. 
Between 1000 and 2000 ft. there are the subalpine 
species, and above 2000 ft. the alpine and arctic 
species. 
Hence altitude may be said to affect plants and 
their distribution. 
Much, again, depends upon the nature of the soil. 
The soil with the subsoil is derived from the rock 
beneath, and of such rocks or geological formations 
there are a great number, but the soils resulting 
from them may be resolved into half a dozen types. 
There are clays and loams, coarse sandstones and 
sands, siliceous rocks, limestone and chalk, peat, 
humus, and saline soil. 
Asa whole each soil is found to be characterised 
by the occurrence of a certain type of tree which 
forms a natural plant-formation, with a scrub and 
ground flora peculiar to it. Thus on clays and 
loams the pedunculate variety of the Oak is found, 
with a coppice of Hazel below and associations (that 
is, smaller communities of plants than the plant- 
formation), of Bluebell, and later Bracken, with 
smaller societies of other plants, such as Wood 
Spike Rush, etc. And on limestone or chalk there 
