12 
INTRODUCTION. 
Both range widely through Britain, and are about equally frequent, holding an 
intermediate place between the rare and the common plants. The Opliioglossum 
prevails chiefly in England, decreasing in frequency northward. The Botrychium, 
on the contrary, is abundant on the hills and moors of the north, and becomes a 
rare plant in the south, and especially in the south-east of England. Ophioglos- 
sum ranges from the south of England, as Devon and Sussex, northward at least 
to Moray ; and, if we may rely upon Barry’s ‘ History of Orkney,’ to those 
islands also. The Botrychium is scarce on the south side of the Thames and 
Bristol Channel, but is stated to grow in North Devon and in Hampshire, though 
not introduced into the Flora of the former county. The stations in the south 
of England of course indicate that both species will grow at a low elevation, and 
remote from the mountain tract, even in the warmest part of Britain ; and both 
also thrive amidst the mountains in the north of England and Scotland ; but the 
Botrychium probably rises to a much greater height on the hills, as it occurs on 
the Breadalbane mountains, near Killin, at the estimated height of 1000 yards, 
whilst no very high elevation for the Ophioglossum appears on record. Of the 
two, the Botrychium is the least frequent, or seems to be so on account of its 
more boreal and Alpine tastes.” — Mr. Watson’s MS. 
ISOETACE^E. 
(Containing Isoetes only.) 
Lycopodiacea, Lind., Decan., Brongn . ; — Marsileacea, Hook . ; — Miscel- 
lanea, Part of Rhizosperma, Rhizopterides, Hydropterides, &c. 
The genus Isoetes has in all arrangements of British plants been associated with 
Pilularia, on account of their both being water plants, both having round and 
filiform leaves, and bearing two kinds of grains or capsules ; but, except in these 
particulars, they are totally different from each other. The roots of Isoetes are 
tufted, composed of round, smooth, branched fibres ; its leaves grow from a 
crown, and consist of four hollow tubes, united together ; but so brittle are they, 
that the cells are often broken into each other by the pressure used in drying the 
plants, and therefore the leaf generally appears a single tube, divided into cells 
by transverse dissepiments. It is so swelled at the base that the joint or cell next 
the root becomes a receptacle for the fruit, which being of two kinds, as in 
Pilularia, are considered analogous to them ; viz. pollen and spores respectively, 
the former in fine powdery grains in the inner leaves — the real spores or seeds 
being confined to those on the outside of the plant. These larger globules are not 
single round spores, but each is composed of three or four spores, joined 
together. Their junction shows at the apex three radiating lines, which were for a 
long time considered as the hilum of the seed. The attachment and arrangement 
of the globules within the receptacle are very beautiful and remarkable. The 
