A HISTORY OF BERKSHIRE variety only of B.fcetidd), Calamintha Nepeta, Daphne Mezereum, Polygonum dume forum, Asarum (?), Orchis Simla (? extinct), Ornithogalum pyrenalcum, Orchis mllitarls^ Leucojum eestivum, and Potamogeton compressum (P. Friesii) . In the two groups mentioned last there are several species which have much too low census numbers, and among these we may mention Crepls taraxaclfolla and C. biennis, Ulex minor ( U. nanus] , Eropbila prcecox, Potamogeton compressum (P. zosterifolius, P. Friesii (P. compressum) and Polygala calcarea, Of the 58 species said to be limited to a single county in Topogra- phical Botany we have not a single example, for Rosa septum (R. agrestls] has now been found in several, but I have discovered one endemic species limited to Berkshire, namely Potamogeton Drucei, Fryer, which is as yet known from no other locality in the world. If we compare the flora of Oxfordshire with that of Berkshire we shall find that the two counties are more dissimilar than their contiguity and physical characters would have led one to expect. Oxfordshire possesses a few interesting species not known to occur in Berkshire, and which are chiefly round on the oolite and forest marble, geological formations which do not extend into Berkshire. These species are Thlaspl pe rfo/iafum, only found as an introduced plant by the railway near Denchworth in Berkshire ; the limestone polypody (Phegopterls calcarea) and the spider orchid (Ophrys aranifera), very rare; the green hound's tongue (Cynoglossum. montanum) ; the woundwort (Stacbys germanlcd) ; and the meadow sage (Safola pratensis] , but this is found in solitary examples in Berkshire and possibly may be introduced. The once extensive fen district of Otmoor in Oxford has yielded three species not known in Berkshire, namely the marsh sowthistle (Sonchus palustrls) , the fen violet (Viola per sl- ccefolia) and the marsh dock (Rumex limosus), but the two latter have not been met with recently. The Oxfordshire Chilterns have the sword- leaved helleborine (Cephalanthera ensifolia), the oak fern (Phegopterls Dryopteris) and the mountain cat's-foot (Antennaria dlolca), but all three are excessively local in Oxfordshire. Potamogeton declplens, Rubus PoiveHii, R. fusco-ater, Teucrlum Chamcedrys, Aristolochla and Fesfuca hetrophylla. The last three species more or less naturalized in Oxford- shire are either not recorded or, as in the case of the birthwort, recorded only on very old authority for Berkshire. A few local plants are more plentiful in Oxfordshire than in Berk- shire ; among them are Helleborus fcetidus, H. viridis, Cnicus eriophorus and Colchicum, which are not only more frequent but have a wider dis- tribution in Oxfordshire than in Berkshire. Pyrola minor, which is widely distributed in the woods of the Oxfordshire Chilterns, appears to be absent from similar woods on the Berkshire side of the Thames, though it is found in two localities on the Bagshot sands in the latter county. The Berkshire flora, as will have been seen by the enumeration already given, is larger than that of Oxfordshire, the extensive heaths and bogs 36
