IV.  FLORA AND FAUNA

In his Cybele Britannica, H. C. Watson divided Britain into eighteen botanical provinces of which the Thames and the Ouse occupy the whole of the S.E. of England.  The greater part of Hertfordshire is in the Thames province and a small portion in the N. is in that of the Ouse.

In Pryor’s Flora of Hertfordshire, published by the Hertfordshire Natural History Society in 1887, which should be referred to for full information on the botany of the county, these botanical provinces are again divided into districts, the Ouse into (1) Cam, (2) Ivel; and the Thames into (3) Thame, (4) Colne, (5) Brent, (6) Lea; both the larger provinces and the smaller districts thus being founded on the natural divisions of a country, drainage areas or catchment basins.

In the following brief notes a few of the rarer or more interesting flowering plants of each district are enumerated.

1. The Cam.—­This is the most northern district.  It is almost entirely on the Chalk and is very bare of trees.  The few plants which are restricted to it are very rare.  A meadow-rue, Thalictrum Jacquinianum, and the cat’s foot (Antennaria dioica) occur only on Royston and Therfield Heaths; Alisma ranunculoides and Potamogeton coloratus only on Ashwell Common; and of the great burnet (Poterium officinale) the sole record is that of a plant gathered near Ashwell in 1840.

2. The Ivel.—­This district is S.W. of that of the Cam, and the Chalk Downs of that district are continued through it.  Its rarer plants are Melampyrum arvense, which occurs only in one spot S. of Ashwell; Smyrnium olusatrum, which has been found near Baldock and Pirton; and Silene conica, which was found near Hitchin in 1875.  The white helleborine (Cephalanthera pallens), the dwarf orchis (Orchis ustulata), and the musk orchis (Herminium monorchis) occur on the Chalk Downs.

3. The Thame.—­A very small tongue-like protrusion[a] of the extreme W. of the county, in which are the Tring Reservoirs.  Two of the species confined to the district, Typha angustifolia and Potamogeton Friesii, are water-plants which occur only in these reservoirs or in the canals which they supply.  A rare poplar, Populus canescens, grows by the Wilstone reservoir, and the man-orchis (Aceras anthropophora) on terraces cut in the Chalk near Tring.

4. The Colne.—­A large district, comprising almost the whole of the western portion of the county. Diplotaxis tenuefolia, Silene nutans, and Hieracium murorum grow only on old walls in St. Albans.  Colney Heath is our only habitat for a very rare loosestrife, Lythrum hyssopyfolium, and also for Teesdalia nudicaulis, while there is but one other locality, a different one in each case, for four of its plants, Radiola linoides, Centunculus minimus, Cuscuta epithymum, and Potamogeton acutifolius.  The pasque-flower (Anemone pulsatilla) grows abundantly on the Chalk slopes near Aldbury.  The rarer orchids of the district are the bog-orchis (Malaxis paludosa), the narrow-leaved helleborine (Cephalanthera ensifolia), and the butterfly orchis (Habenaria bifolia).