154 THE ESSEX NATURALIST
References
Barker, G. M. A. (1972). Wildlife Conservation in the Care of Churches and
Churchyards. Church Information Office. London.
Ferry, B. W., Baddeley, M. S. and Hawksworth, D. L. (ed.) (1973). Air
Pollution and Lichens. London.
Hawksworth, D. L., Rose, F. (1970). Qualitative scale for estimating sulphur
dioxide pollution in England and Wales using epiphytic lichens. Nature, 227:
145-148.
Hawksworth, D. L., Rose, F. & Coppens, B. J. (1973). Changes in the lichen
flora of England and Wales attributable to pollution of the air by sulphur
dioxide. In: Ferry, B. W., Baddeley, M. S. and Hawksworth, D. L. (ed.)
Air Pollution and Lichens: 330-367. London.
James, P. W. (1965). A new check-list of British lichens. Lichenologist, 3: 95-153.
James, P. W. (1966). A new check-list of British lichens: Additions and correc-
tions—1. Lichenologist, 3: 242-247.
Laundon, J. R. (1958). The lichen vegetation of Bookham Common. Lond. Nat.
37: 66-79.
Laundon, J. R. (1967). A study of the lichen flora of London. Lichenologist, 3:
279-327.
Laundon, J. R. (1973). Changes in the lichen flora of Bookham Commons with
increased air pollution and other factors. Lond. Nat. 52: 82-92.
Warren Spring Laboratory. (1972). National Survey of Air Pollution 1961-71.
1. H.M.S.O., London.
Figure 1 Urbanisation and main localities referred to in the text. 1, Galleywood
Common (52/703019); 2, Thrift Wood, Bicknacre (52/791018); 3, Railway bridge
and embankment, Hutton (51/627967); 4, 6 Fairview Avenue, Hutton (51/
631949); 5, All Saints' Church, Hutton (51/635943); 6, Havering's Grove
(51/651945); 7, Great Cowbridge Grange (51/653953); 8, 117 Norsey Road,
Billericay (51/687960); 9, Norsey Farm, Billericay (51/688961); 10, Norsey Wood,
Billericay (51/688955); 11, Botney Hill Farm, Little Burstead (51/653917); 12,
Dunton Lodge, Herongate (51/644911); 13, St Mary's Church, Little Burstead
(51/668915); 14, Congregational Church, Billericay (51/675943); 15, Brock Hill
(51/738964); 16, All Saints' Church, Rettendon (51/770960); 17, St. Mary's
Church, Runwell (51/754944); 18, Railway bridge, near Dunton Hall (51/658881);
19, Disused barracks, Langdon Hills (51/668863); 20, Westley Heights, Langdon
Hills (51/688867); 21, One Tree Hill (51/697861); 22, North Benfleet (51/753896);
23, Pitsea Marsh (51/738868). ■, Urban areas;------, boundary of area studied.