BOTANY NOTES ON THE BOTANICAL DISTRICTS, WITH LISTS OF THE RARER PLANTS OF EACH DISTRICT In the Flora Hertfordiensis of Webb and Coleman (1849) Hertfordshire was divided into botanical districts founded on the river-basins. The three main districts were the Lea, the Colne, and the Ouse, each of these being divided into sub-districts representing the tributaries of these rivers, and the number of such sub-districts were twelve. In a paper read before the Watford (now Hertfordshire) Natural History Society in 1875 * the late Alfred Reginald Pryor recognized the primary separation of the county into the catch- ment-basin of the Ouse on the north and that of the Thames on the south, ' districts which,' he said, ' in the floras of the future, will probably be entirely dissociated from each other and united respectively to those portions of the same river-system with which they are naturally connected, but which are now scattered among the southern and eastern shires.' He then divided the Ouse district into the Ivel and Cam ; and the Thames into the Thame, the Colne with five sub-districts, the Brent, and the Lea with six sub-districts, making sixteen districts in all. He afterwards found this subdivision to be impracticable from the impossibility of assign- ing many of the old records to these districts, and he therefore abandoned the sub-districts of the Colne and Lea and finally left the scheme thus T T-U r ( ! The Cam I. The Ouse . , T . 2. The Ivel II. The Thames 3. The Thame 4. The Colne 5. The Brent 6. The Lea This is the division of the county which was adopted in his Flora of Hertfordshire published in 1887, a few years after his death. As this work is the basis of the present article on the botany of Hertfordshire, the above division is necessarily followed. 8 DISTRICT I. THE CAM This is the most northern district. It is bounded on the east by Essex, on the north by Cambridgeshire which divides it into two, on the west by Bedfordshire, and on the south by the Ivel and Lea districts. A stream called the Wadrington Brook, which while in Herts is little more than a ditch, flows through the eastern division of the district, and through the western division flows the Rhee, which rises from copious springs in the Totternhoe Stone at Ashwell, is joined at the extreme north of the county by the Ruddry Brook, and joins the Cam a little south of Cam- bridge. The district is almost entirely on the Chalk, a small portion on the north-east being on the Gault. It is very bare of trees and is marked by the absence of hygrophiles (see p. 39). In the eastern division are the Royston Downs, rising to about 500 feet above sea-level. The few species which are restricted to this district are very rare. Thalictrum jacquini- anum and Antennaria dioica occur only on Royston and Therfield Heaths in the eastern division ; ARsma ranunculoides and Potamogeton cokratut only on Ashwell Common in the western division ; and of Poterium officinale the only record is that of a plant in Coleman's herbarium gathered in the neighbourhood of Ashwell in 1840. The rarer plants of the district are RANUNCULACE* FUMARIACR* TbaRetnm Jacqmnianum, Koch Fumaria parviflora, Lami. Anemone pulsatilla, L. _ Vaillantii, LnuL Helleborus foetidus, L. PATAVERACE* Papaver hvbndum, L. Iberis amara, L.
l? n the Botanical Work of the Past Season,' 'Trans. Watford Nat. Hist. Sot. vol. i. pp. 65-77.
The names of the plants which only occur in one .listrict are printed in italics. 51
