INTRODUCTION. 
13 
theca when cat across exhibits a number of transverse bars, to which the spores 
are attached by little foot-stalks, there being four on each bar, set crosswise with 
each other. The leaves are said to have stomata, and to be circinate 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. 
DISTRIBUTION. — “ The single species of this order, a submerged aquatic, 
can of course grow only where there is a suitable home in the waters. Probably 
it may require also that the water be of low temperature in summer, since most 
of its habitats are the Highland lakes ; although, according to Mr. Griffith, it 
extends southward into Shropshire. There are very few other English and Welsh 
comities that produce it, and these few are all mountainous ; namely, Caernar- 
vonshire, Denbighshire, Cumberland, and Northumberland. In most counties 
north of the Firths of Forth and Clyde, we may find it in the lakes, some of them 
being situate 600 yards or upwards above the sea.” — Mr. Watson’s MS. 
MARSILEACEvE. 
(Including only Pilularia.) 
Part of the Marsileace.®, Br., Brongn., Decan., Hook., Grev . ; — Hvdrop- 
terides, Willd.; — Rhizospermje, Roth ; — Rhizopterides, Mart .; — 
Radicalia, Hoffrn . ; — Riiizocarp/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 petioles, as some 
call them, are curled up in vernation, as in the Polypodiacese, have stomata upon 
their cuticle, and a cross section of them shows that they are divided longitudinally 
into various cells, separated from each other by septa radiating from the centre, 
and forming by their union a kind of axis, composed of dotted ducts or spiral 
vessels. Thus the structure of the leaf although without a central cavity, is in 
a great degree analogous to that of the stem of the Equisetacese, and also to the 
leaf of Isoetes. The roots and stems are similarly constructed. 
The thecae are round, coriaceous, brown, hairy, and divided into four cells. 
They contain globules of two kinds ; the first small round grains, said to be pollen, 
but which others consider as abortive capsules. These occupy principally the 
upper part of each theca ; in the lower are found much larger grains, which are 
oval, rather pointed, contracted in the middle, and at their apex have a conical 
projection. These are true spores, and as well as the former are contained in 
membranous bags. Since writing the above, a very valuable paper by Mr. 
Valentine, upon “ The Germination and General Structure of Pilularia,” was 
read before the Linmean Society, and is to be found in their “ Transactions,” 
