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Rh Near Water Stratford the pondweed Potamogeton alpinus grows in the river, and the marshy ground near yields Polygonum mite. In the low fenny ground near Simpson the celery (Apium graveolens) is probably native. The reed-mace (Typha angustifolia) and a somewhat intermediate form grows near Bletchley, and in arable fields a form of the bur parsley (Caucalis nodosa var. pedunculata) grows with the umbels distinctly stalked. By a brook near Salford the willow herb (Epilobium roseum) grows with some hybrids with E. parviflorum and E. obscurum, and a willow which is a triandra hybrid. In the Moulsoe woods the violet {Viola sylveitris) is frequent.

The sawwort (Serratula tinctoria) grows in some wet meadows near Brickhill, and the local Scirpus sylvaticus is also found.

Near Soulbury in some marshy ground, partly woodland, there is a luxuriant growth of the great horsetail (Equisetum maximum) the marsh lousewort (Pedicularis palustris), the sedges Carex distans, C. fava, C. echinata, the cotton grass (Eriophorum angustifolium), and the small club rush (Scirpus setaceus).

Near Linslade there is an abundant growth of a rush which by many botanists is considered to be a hybrid of Juncus glaucus with J. efusus, i.e. the J. diffusus, and with it grows in an unusual station the heath stitchwort (Stellaria graminea) as a very broad-leaved form.

There are not many introduced species in this district; such as occur are chiefly near flour mills, where the siftings of foreign wheat containing seeds of such plants as Brassica elongata, Setaria viridis, Sisymbrium altissimum occasionally germinate in the vicinity.

The railway lines have been the means of bringing in the rocket (Diplotaxis muralis) and the eastern vetch (Vicia villosa), which grows near Leighton Buzzard.

The winter heliotrope (Nardosmia or Petasites fragrans) is naturalized near Wavendon, and in waste places about Woburn Sands Atriplex hortensis var. rubra, Oxalis corniculata, Hesperis matronalis, grow.

This district takes its name from a stream whose waters in part rise from the Oolitic rocks of Quainton, partly from Stewkley Hill and in part from the Cretaceous hills near Tring, and in its feeders in their early course cut across several different strata, uniting near Aylesbury. The main stream passes through Lower Winchenden to Notley Abbey, where a small brook which has come from Brill and Waddesdon joins it, and just before reaching Thame it is reinforced by the Ford brook which has drained the Gault meadows from Bishopstone to Tythrop. There are also several brooks which issue from the base of the Portland stone on the western side of Brill and Chilton and flow into Oxfordshire, joining the Thame in the neighbourhood of Shabbington and Worminghall.

The Thame district of Buckinghamshire has its counterpart in my Flora of Oxfordshire, but in the plan adopted here for Bucks there is included a small piece of country which, belonging as it does to the Ray drainage, had a separate district No. 4 in my Flora of Oxfordshire, and belongs to the Cherwell basin. It would have been more accurate to make the portion of Bucks drained by the Ray a district or a sub-district, but the limitations of it shall be described, and as it is of small extent and since it closely resembles in soil the adjacent country drained by the tributaries of the Thame, and because the Cherwell itself belongs to the main drainage of the Thames, there appear no sufficiently cogent reasons for keeping it distinct.

The Thame district is thus defined: On the north it is bounded by the Ouse district already described, that is from Poundon to Stewkley. On the west it is limited by the county of Oxford, from near Poundon to Piddington and Brill; then the boundary passes to the west of Boarstall, so that the interesting decoy and the remains of the fortified house are included in Bucks; it then traverses a very secluded sylvan district by Studley and Shabbington Wood to Worminghall and Thame, the stream itself for the last four miles having been the boundary. From Tythrop the boundary is an artificial one. The separating line from Oxfordshire is traced to the Common Leys near Towersey, and then by Shittle Green to Bledlow Cross, where its western boundary to Radnage is my division No. 7, the Lower Thames of my Oxfordshire Flora. It then takes the summit-level of the Chilterns in an easterly direction towards Lacey Green, the southern boundary being now the water parting of the Thame on the one side, and the tributaries of the Wycomb stream on the other as far as Hampden, when the water parting of the tributaries of the Amersham water and the Chess replace that of the Wycomb stream as far as the border of Hertfordshire near Tring