ulgare_, var. _multifidum_; _Athyrium filixfaemina_[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_ (_Hepaticae_) forty-four species are known to occur;
and the Stoneworts (_Characeae_) are represented by seven species--two of
_Chara_, two of _Tolypella_, and three of _Nitella_.

_The Algae_ have been pretty fully investigated, especially the
_Diatomaceae_, of the 252 species of Algae known to occur in the county,
156 belonging to that interesting family of microscopic plants. As an
illustration of their minute size it may be mentioned that a single drop
of water from the saucer of a flower-pot at Hertford, mounted as a
microscopic slide, was found to contain 200,000 separate frustules of
_Achnanthes subsessilis_, and it was estimated that these occupied only
one twenty-fifth part of the drop. Both species of _Chlamidococcus_ (the
old genus _Protococcus_), _C. pluvialis_ and _C. nivalis_ occur; and
the pretty _Volvox globator_ has frequently been found.

Of _the Lichens_ much less is known, only sixty-seven species having
been recorded. The most noteworthy are _Calicium melanophaeum_, found on
fir-trees in Bricket Wood; _Peltigera polydactyla_, on moss-covered
ground in Oxhey Woods, Watford; _Lecanora phlogina_, in the Tunnel
Woods, Watford; and _Pertusaria globulifera_, on trees in the same woods
and also in Bricket Wood. As woods in the vicinity of Hertford and of
Watford only have been searched for lichens, our list ought to be
largely increased by investigation in other parts of the county.

Of _the Fungi_ our chief knowledge is derived from lists of species
collected at Fungus Forays of the Hertfordshire Natural History Society
and from records of the Mycetozoa by Mr. James Saunders. The number of
species re