Loddon or Lower Thames' of my Flora of Berkshire, except that as the Bagshot Sands are not represented in our county the botany is of a much less interesting character.
The ' Thames ' district is circumscribed by the following boundaries : On the north-west the boundary line is the water-parting of the Wycombe streams from those which drain into the Thame, but as this is a chalk area with the drainage chiefly underground it is difficult to make a definite line of demarcation. We trace it as best we may from Hampden by Loosely Row to the Oxfordshire county boundary near Radnage, and then that arbitrary division is followed in its eccentric course to the south of Stokenchurch by Cadmore End, Ibstone, Hollandridge, Stonor Park, to Middle Assendon and Henley Park, where it touches the river Thames. From this place to Old Windsor the river divides the district from Berkshire, and all that portion of Berkshire on the opposite side is included in the district No. 5 of my Flora of that county. Opposite Runnymede, from the point where Surrey replaces Berkshire, the boundary of our district is again rather artificially drawn along the Wyrardisbury, or to use the modern spelling, Wraysbury road, to Langley station on the Great Western Railway, and thence by the side of Langley Park to the north-west of Alderbourne Bottom and passing to the north of Fulmer, but again turning in a south-eastern direction it skirts Gerrard's Cross Common (which is included in this district), and then passes along the high ground above Chalfont St. Peter's ; taking in Later's Green Common and Seer Green, it proceeds by Ongar Hill and Penn House through Penn Woods to Great Kingshill, then to Prestwood, and eventually joins the Thame district at Hampden.
The name is given to the district because the river Thames flows for so long a distance along the western and south-western side, and hence necessarily drains a considerable portion of its area, but there is also a subsidiary stream, which might be utilized to form another district were it considered advisable, but as both streams drain very similar country and the geological strata in both are similar, and as the area is not unwieldy, the portion drained by the Wye or Wycombe Brook is incorporated with the Thames. The Wye issues from the southern slopes of the chalk, and the valley it occupies from West Wycombe to Bourne End where it flows into the Thames is utilized for the Wycombe branch of the Great Western Railway. The Wye is a pretty chalk stream with, where unpolluted by man, clear sparkling water, and in its course flows so swiftly that in more places than one it is markedly different from our normally sluggish streams, for it can murmur as it flows by Loudwater, a significant name. Watercresses are extensively grown in the stream, and several large manufactories of paper have been established on its banks on account of the clearness of its waters.
The country comprised in this district is very pleasant and fairly diversified, but the strata represented in it are wholly Cretaceous or belong to the Eocene formations of the Reading Beds and the London Clay, with extensive beds of High and Low Level Alluvium.
There are great tracts of woodlands on the Chalk, the chief constituents of which have been enumerated under that heading, and there are also extensive, and we are glad to say at present unenclosed, commons with an attractive flora, as well as the dry fields, and occasional grassy banks of the Upper and Lower Chalk areas. The London Clay is sufficiently impervious to make marshy ground even at considerable elevations, as at the top of Lane End Common, nearly 600 feet in altitude. In that place and on Moor Common we have many interesting species, several of which have not been found in the county north of the Chilterns ; they include the petty whin (Genista anglica), which is very abundant, the dwarf willow (Salix repeni), the upright pearlwort (Cerastium quaternellum, better known under its old name of Mœnchia), the pearlwort Sagina ciliata, the water milfoil (Myriophyllum alternifolium), the water purslane (Peplis Portula), the water honewort (Apium inundatum), the lousewort (Pedicularus sylvatica), the clovers Trifolium filiforme and T. striatum, the lady's traces (Spiranthes autumnalis or Gyrostachis), the spotted orchid (Orchis ericetorum), the small crowfoot (Ranunculus parviflorus) ; and Burnham Beeches is one of the few localities for the deer's grass (Scirpus cæspitosus), the club rush (Eleocharis multicaulis), the white beak rush (Rynchospora alba]), for the cross-leaved heath (Erica Tetralix), the Lancashire asphodel (Narthecium ossifragum), the marsh St. John's wort (Hypericum eludes), for the charad (Nitella translucent), the bladder wort (Utricularia major or neglecta). It is also the home of the sedges Carex pulicaris, C. echinata, C. flava, C. panicea, C. paniculata, C. rostrata, C. binervis, C. pilulifera, C. leporina ; the pondweeds Potamogeton polygonifolius and P. pusillus, the bog-bean (Menyanthes trifoliata), the cotton grass (Eriophorum angustifolium), the grasses Molinia varia, Festuca ovina var. paludosa, the hawkweeds Hieracium boreale, H. sciapbilum and H. umbellatum, the marsh violet (Viola palustris), the butterwort (Pinguicula vuigaris), the sundews Drosera rotundifolia and D. intermedia or longifolia but not D. anglica, the
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