species, yet there is an even larger portion coloured as chalk on the geological map, which is really covered with a reddish earth to which the name of ' brick-earth ' is given, and when this is present it so modifies the vegetation that a very dissimilar flora will be found from that where the chalk itself forms the surface soil. The chief tree in the woods is of course the beech, with hornbeam; and occasionally the cherry; and the ash is not unfrequent in open situations, while in some of the more clayey and sheltered places the oak is found. The plant of special interest is the local coral-root (Cardamine bulbifera), the Dentaria bulbifera of Linnæs, so named from the curious bulbils present in the axils of the leaves. These bulbils drop off and form another plant, thus enabling it to perpetuate itself without seeding, which as it grows in rather dense shade is not of frequent occurrence. The plant prefers to grow where there are plenty of loose flints and leaf-mould in hilly woods, and although extending into Herts and Berks has not yet been found in the woods of the Oxfordshire Chilterns. The helleborines Epipactis latifolia and E. violacea are found as well as occasionally the herb Paris (Paris quadrifolia), the gromwell (Lithospermum officinale), the large woodrush (Luzula or Juncoides syhatica), the lady's mantle (Alchemilla vulgaris), the beautiful wood vetch (Vicia sylvatica), the very rare and interesting shrub Daphne Mezereum, as well as the spurge laurel (D. Laureola), the mountain speedwell (Veronica montana), the sedges Carex pallescens and C. strigosa, the grasses Milium effusum and Meicea uniflora, the toothwort (Lathrea Squamaria), the willow herb (Epilobium angustifolium), besides Pimpinella major.
The Chalk in this southern area, although so frequently obscured by the deposits alluded to, is at intervals the surface rock, especially on the sides of the dry valleys or deep road-cutting. When this is the case the vegetation at once changes in character, and in the calcareous woods we have the yew (Taxus baccata), the juniper (Juniperus communis), the hornbeam (Carpinus Betulusll), all certainly native; the wood barley (Elytmus europceus), which can also grow where there is some covering to the chalk; the wood rush (Juncoides [Luzula] Forsferi), and much more locally the Solomon's seal (Polygonatum multtflorum), so much rarer here than in the woods on the Berkshire chalk hills, and this again prefers some coating either of leaf-mould or even brick-earth; the rare military orchid (Orchis militaris), one of the chief botanical treasures of the county, but now much less frequently occurring than was formerly the case, and chiefly on the borders of woods; the mountain St. John's wort (Hypericum montanum), the tutsan (H. Androscemuni), the two hellebores Helleborus viridis and H.fætidus, but both locally; and with a still more restricted distribu- tion the oak fern (Phegopteris Dryopteris) and the limestone polypody (P. calcarea); a hawkweed (Hieracium murorum var. pellucidum), and more commonly the ploughman's spikenard (Inula Conyza). The stinking gladdon (Iris foeti dissima), the butcher's broom (Ruscus aculeatus), the wild licorice vetch (Astragalus glycyphyllos), the blue toadflax (Linaria repens) are chiefly found on the chalk hills overlooking the river. On the grass-covered downs the musk orchid (Herminium Monorchis) and the large
38
