Heordshire | Page 6

having 28 inches and the latter 24½. The small portion of the
river-basin of the Great Ouse which is within our area has rather less
rain than the average for the county.
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).
5. The Brent.--The smallest district, a protrusion[b] of the county in the
S. entirely on the London Clay, and chiefly interesting owing to the
presence of Totteridge Green and its ponds. In these ponds grow the
great spearwort (Ranunculus lingua) and the sweet-flag (_Acorus
calamus_), the former, however, not being indigenous. The star-fruit
(Damasonium stellatum) formerly grew on Totteridge Green, and
Chenopodium glaucum at Totteridge, but neither has lately been seen.
6. The Lea.--The largest district, comprising the whole of the E. of the
county. The London rocket (Sisymbrium irio) occurs only in the old

towns of Hertford and Ware; the true oxlip (Primula elatior) near the
head of the River Stort; a very rare broom-rape, Orobanche cærulea, at
Hoddesdon, where it is parasitic on the milfoil; and an almost equally
rare bedstraw, Galium anglicum, on an old wall of Brocket Park. A rare
trefoil, Trifolium glomeratum, is known only at Easneye near Ware;
and Hatfield Park is our only locality for the water-soldier (_Stratiotes
aloides_) except where it has evidently been planted. Two species,
usually of rare occurrence, Polygonum dumetorum and _Apera
spica-venta_, are frequent in the district.
The indigenous flowering plants of Hertfordshire number 893 species,
679 being Dicotyledons and 214 Monocotyledons. If to these be added
199 aliens, etc., the total number of species recorded is brought up to
1,092. The flora is essentially of a southern type, the northern species
being few in number. Owing to the dry soil, xerophiles largely prevail
over hygrophiles.
The Ferns and their allies the horsetails and clubmosses are not well
represented, both the soil and the air of the county being too dry for
them. Another cause for the present