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Rh Besides these above named varieties, many hybrids and over 120 species not natives or of casual occurrence, or planted in the county, have been observed.

If the London Catalogue of British plants be adopted as the standard of specific limitations we may say that the total number of British species is now about 2,000, but of these nearly 250 are not native species, 144 are confined to the neighbourhood of the sea, while at least 200 are a species either of northern latitudes, or are not found so far south as Buckinghamshire, except in mountainous situations ; 17 are confined to Ireland, about 20 to the Channel Isles, and a few are extinct.

After making these deductions about 1,350 species remain which might occur in the county, but such is not found to be the case ; for although our knowledge of the county flora is incomplete, yet it is not to be expected that more than 50 species will be added to the list here given, however painstaking may be the work. As compared with the bordering counties, however, Buckinghamshire is richer in species than almost any except Berkshire.

The paucity of lacustrine species is one of the features which characterize the botany of the county, and this is accounted for by the large extent of country occupied by the Cretaceous beds and the absence of large sheets of water such as the Norfolk broads or Salopian meres and the marshy vegetation which surrounds them, but the chalk, limestone, and heath plants are fairly well represented. The three most inter- esting species are probably the pig-nut (Carum Bulbocastanum), which is limited to Bucks, Herts, Beds and Cambridgeshire ; the military orchis (Orchis militaris), limited to Berks, Oxford, Herts and Middlesex, and the box (Buxus sempervirens), which is so well established in two places on the Chilterns, and by some authors is even considered to be native. The other characteristic species are the coral-root (Cardamine bulbifera), so common in several woods on the chalk ; and the beech (Fagus sylvatica), which is the principal tree over a large area of the Cretaceous measures and is of considerable economic value.

A few other species are rather common in Buckinghamshire but are local or rare in many British counties. Amongst these are the calamint (Calamintha Nepeta or parviflora), the large burnet-saxifrage (Pimpinella major), and the candytuft (Iberis amara). The woods of the north have the grass Calamagrostis epigeios, the commons have the dwarf gorse (Ulex minor), and in the south the silver cinquefoil (Potentilla argentea) is not uncommon.

A short sketch of the geology is first given with especial reference to the influence the various strata have upon the botanical features of the