The Ecology of Calluna vulgaris. 
22 7 
PRELIMINARY OBSERVATIONS ON 
THE ECOLOGY OF CALLUNA VULGARIS ON THE 
WILTSHIRE AND BERKSHIRE DOWNS. 
By M. C. Rayner, B.Sc. and W. N. Jones, M.A., 
Soil Analyses by J. W. Tayleur, B.Sc. 
ALLUNA VULGARIS, associated with other more or less 
typical heath plants, occurs sporadically on the chalk-downs 
of the South of England, sometimes in sufficient abundance to 
form a conspicuous feature of the vegetation. 
In a few places on the Berkshire and Wiltshire Downs 
the heather grows luxuriantly to a height of 2—3 feet, giving rise 
to well-defined communities from which the characteristic plants 
of the surrounding vegetation are excluded ; more often it occurs 
mixed with grasses and other species, some of which are alien 
to the typical Down flora of the neighbourhood. 
This heath flora is found chiefly on the more elevated part of 
the Downs, often as high as, or above 700 feet, the distribution 
varying from scattered patches over large areas to smaller and very 
well-defined communities which contrast sharply with the surrounding 
vegetation, the tendency to spread being apparently determined by 
definite factors. 
It seems probable from their distribution and association with 
the characteristic plants of the locality, that the heath plants are 
invaders, which in some cases, e.g., Calluna, can compete successfully 
with the original inhabitants. 
The presence of these plants on the chalk uplands is apparently 
correlated with the fact that in Wilts and Berks, as elsewhere, 
the chalk is locally overlaid by clay-with-flints. A possibility of 
small tertiary outliers also exists, the upper beds of which form 
characteristic heaths and commons in other parts of Berkshire. 
Clay-with-flints is a general name for a superficial deposit, varying 
in character in different localities; in the district under con¬ 
sideration usually a heavy yellowish clay containing flints. Older 
observers regarded it as derived from weathering of the chalk (1). 
A more recent view holds that the material composing it was derived 
from outlying Eocene tracts during late Pliocene times, broken 
