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 scarcity of ferns is the proximity
of Hertfordshire to London, for they have been uprooted and taken there
for sale in cart-loads. We have twenty-four species of ferns and
fern-allies, but not one really rare. The principal varieties are
_Scolopendrium vulgare_, var. _multifidum_; _Athyrium filixfæmina_[c],
var. _convexum_; and _Polypodium vulgare_, var. _serratum_. _Equisetum
silvaticum_ is our rarest horsetail; and our only clubmoss is
_Lycopodium clavatum_.

_The Mosses_ are much better represented than the ferns, 175 species
having been recorded. The bog-mosses are represented by six
species--_Sphagnum intermedium_, _cuspidatum_, _subsecundum,
acutifolium_, _squarrosum_, and _cymbifolium_. _Tetraphis pellucida_
occurs in Sherrard's Park Wood, and _Polytrichum urnigerum_ in Hitch
Wood. _Seligeria pusilla_ has been found in an old chalk-pit in Brocket
Park, and _S. paucifolia_ on chalk nodules in the Tunnel Woods near
Watford. _Campylopus pyriforme_ occurs in Berry Grove Wood, Aldenham,
and _C. flexuosus_ in Dawley's Wood, Tewin.

Of _the Liverworts_ (_Hepaticæ_) forty-four species are known to occur;
and the Stoneworts (_Characeæ_) are represented by seven species--two of
_Chara_, two of _Tolypella_, and three of _Nitella_.

_The Algæ_ have been pretty fully investigated, especially the
_Diatomaceæ_, of the 252 species of Algæ known to occur in the county,
156 belonging to that interesting family of microscopic plants. As an