210 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
the intermediate conditions these offer between moisture and drought. 
But some, especially Krause, believe that it is due to the much greater 
influence man has had on the land in these western regions. Firstly, 
by means of deforestation, and, secondly, by the actual “ cultivation ” 
of the heath by regular burning. Krause concludes that most, but 
not all, Calluna heaths have formerly been covered with trees. His 
exceptions are chiefly regions analogous to Tentsmuir, largely formed 
from blown sea sand. 
Although we cannot yet say how far these ideas are applicable to 
Scotland, still we see enough to understand that man’s influence is a 
very important factor. Heather in most districts is regularly looked 
after by man. If left to itself, it becomes very long and woody, and 
of little good for fodder. According to Grsbner, it ceases to flower 
after fifteen years, and dies out in twenty-four, or thereabout. What 
will happen when it dies out will depend on circumstances. On the 
drier parts of our hills the old heather becomes patchy from the 
growth of lichens (Cladonia). When moisture becomes more con¬ 
stant grasses or sedges may spring up; or in some cases seeds of 
heather may be blown from other parts and regenerate the heather 
area. But it is rarely that we come across heather thus left to itself. 
As a rule, it is regularly burned every few years to provide young tops 
for the grouse. On the burnt part grasses, herbs, and young heather 
from the old roots spring up. The grazing sheep exercise a selective 
influence on the vegetation in favour of the heather, so that it has 
the best chance of surviving and re-peopling the moor. 
We find Calluna heath on a great variety of soils. On Tents¬ 
muir it inhabits a sandy soil; it is very abundant on moorland, both 
wet and dry, particularly on peat. Probably, however, it requires 
recurrent periods of dryness. It also grows well on rocky slopes 
with a loose covering of soil, sufficiently deep to allow its long roots 
to obtain a hold. It is usually regarded as one of those plants which 
especially prefer a siliceous soil. It is essentially a light-loving 
species, and whenever it grows in woods it plays a secondary part. 
The following list of the associates of the heather has been made 
from notes taken on the Grampians, Sidlaws, Fifeshire moors, and 
the Pentlands. From the list have been omitted the species peculiar 
to more marshy spots where Erica Tetralix dominates. 
PLANT ASSOCIATION OF THE CALLUNA HEATH. 
Ranunculus acris, L. 
R. repens, L. 
Viola silvestris, Reich. 
Polygala vulgaris, L. 
Hypericum pulchrum, L. 
Linum catharticum, L. 
Genista anglica, L. 
Lathyrus montanus, Bernh. 
Potentilla silvestris, Neck. 
Galium saxatile, L. 
