VEGETATION SURVEY OF NORFOLK. 
751 
Heathland. 
The two principal types of heathland are Calluna heath and 
heath pasture, both carrying a xerophytic flora ; but whereas 
the purple and brown of ling and fine-leaved heath give tone 
to the former, the green colour of heath grasses pervades the 
latter. As gorse, which is intolerant of lime, occurs in both, 
lime is not necessarily the controlling factor, but rather the 
natural tendency of some soils to form peat. In the com- 
petition for place, grasses become dominant when a certain 
mean standard of aeration and nutrition is reached. Old 
gravel pits show that less favourable ground is colonised by 
plants adapted to rigorous conditions. Mosses and lichens, 
capable of lying dormant through periods of heat and drought, 
and of depending upon the atmosphere and atmospheric dust 
for organic and inorganic food, play an important part by their 
tendency to form a felted carpet detrimental to aerobic soil 
organisms. Stagnation results in a formation of peat which 
saprophytes and certain higher plants living in symbiotic 
relationship with fungi are enabled to utilise as a source of 
nitrogen. 
At Drayton, Felthorpe, Horsford, and St. Faiths the glacial 
gravels carry extensive stretches of Calluna heath ; the waste 
lands of the sandy loams at Stratton Strawless, Honingham, 
Ringland, Frettenham, and Weston carry heath pasture. 
Sudden transitions and the blending of types coincide with 
variations in the subsoil. 
It is probable that many of the arable fields in the light 
land area were heaths until the passing of the Enclosure 
Acts, and the retrogression of arable to fallow is often the first 
stage in the development of heath pasture. On such a field 
west of Church FTill Plantation, Ringland, we found 
Agrostis tenuis and Aira caryophyllea dominant, with 
Holcus lanatus, H. mollis, and the small herbage common to 
heath pasture. 
On a somewhat similar area at Taverham, bracken is 
dominant on the undisturbed heath, with Ceratodon purpureas, 
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