10 
INTRODUCTION. 
particulars, they arc totally different from each other. The roots of Isoctcs 
are tufted, composed of round, smooth, branched fibres ; its leaves grow 
from a crown, and consist of four hollow tubes, 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 as 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 spores joined together vertically ; their junction shows at tlicir apex 
three radiating lines, which were for a long time considered as the liilum of 
the seed. The attachment and arrangement of the globules within the recep- 
tacle are very beautiful and remarkable. The tlicca when cut across exhibits a 
number of transverse bars, to which the spores are attached by little footstalks, 
there being four on each bar, set crosswise with each oilier. The leaves arc 
said to have stomata, and to be circulate in vernation, but neither of these is 
the case. Being a submersed water plant, of course it is without stomata', and 
Martius expressly says, vernation not circinate, but only a little bent, an 
observation confirmed to me by four or five botanists of eminence. 
MARSILEACE/E. 
( Including only Pilularia.) 
Part of the Mars i peaces, Br., JBrongn., Decan., Hook., Grev. ; — IIyrop- 
terides, Willd. ; — Rhizosperm.e, Roth ; — Rhizofterides, Mart. ; — 
Radicalia, Hoffrn.; — Riuzocarp-e, Batsch. 
The stem of Pilularia, which is the only English genus of this order, is 
creeping, and set at intervals with leaves, roots, and fruit. The leaves, or, 
as some call them, petioles, curled up in vernation, as in the Polypodiacca, 
and a cross section of them shows that they are divided longitudinally into six 
triangular cells, separated from each other by septa radiating from the centre, 
and forming by their union a kind of axis, composed of longitudinal ducts or 
spurious trachea, showing that the structure of the leaf although without a 
central cavity, is in a great degree analogous to that of the stem of the 
Equisetaccae. 
The theca are round, coriaceous, brown and hairy, divided into four cells, 
and contain globules of two kinds, the first small round grains, said to be 
pollen, but under the microscope appearing to be merely particles of fecula. 
