FIELD MEETING IN NORTHAMPTONSHIRE The 1984 autumn field meeting was centred on Banbury, a large market town in adjacent Oxfordshire. During the four days, 25-28 October, a large number of sites in the southwest of the county was visited. Northamptonshire (vice-county 32) has an area of 258 482 ha; it is rather narrow, running southwest north east , from the Oxfordshire border in the south to the Soke of Peterborough in the north. The southern half is agricultural and little affected by the industrialization of Northampton or the brickworks around Peterborough, with their associated fluoride emissions. There are likely to be pollution effects from the industrialized north Midlands, including the Birmingham conurbation. Hawksworth & Rose (1970) showed the mean winter sulphur dioxide levels over the county as 70-125 \ig m" 3. Nevertheless, on this visit species from zones 5 and 6 of Hawksworth & Rose were seen and at one sheltered site (Lodge Copse, Hazelborough Forest) Rinodina roboris and Pertusaria hemisphaerica occurred on the trunk of an ancient oak, suggesting that the mean sulphur dioxide levels at this site could now be as low as 40|Xgm" 3 (see site no. 15). The precipitation is more or less constant throughout, ranging from 55-8 to 58-42 cm (22-23 in) in the north of the county to 60-96-63-5 cm (24-25 in) in the south. Lichenologically Northamptonshire straddles two distinct areas, a wet lichen-rich region to the west, and a dry area to the east. The rainfall may be high enough to inhibit distribution westwards of species characteristic of the lowland eastern part of the country, for example Caloplaca ruderum (recorded 1985), which is confined to a few isolated particularly dry sites. Although the rainfall is lower than the 32 in p.a. isopleth, which separates fairly accurately the two isidiate Parmelia species, P. pastillifera and P. tiliacea (Dobson & Hawksworth 1976), it was very interesting to see the more western P. pastillifera in Helmdon and Church Charwelton churchyards. This 32 in isopleth, however, lies within 40-48 km of the southern tip of the county and the porous, ferruginous sandstone on which this species was growing may hold sufficient water to compensate for the dryness. There are few natural outcrops of rock; the underlying rocks of the county are part of the sedimentary, oolitic and lias Middle and Lower Jurassic formations which extend from Dorset to Lincolnshire. These rocks provide a diversity of building materials. Fissile properties and weathering by frosts make roof ' slates', a practice carried on at Collyweston since the fourteenth century. These local building materials form an important substratum for saxicolous lichens. One of the dominant rocks is' ironstone ', a basic ferruginous sandstone quarried most notably at Helmdon; this supports a calcicolous flora, but some of the acidophilic species are also able to colonize it. A member of the Lepraria incana aggr. (divaricatic acid and zeorin) often covers the shaded walls made of this material, producing a spectacular effect. It...