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