20 
INTRODUCTION. 
STRUCTURE. — The stem of Pilularia (see woodcut to this genus), 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 Polvpodiacese, have stomata upon their epidermis, 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. The roots 
and stems are similarly constructed. 
[Reproduction. The thecae are contained in round, coriaceous, brown, hairy 
sporanges, divided into four cells. They contain globules of two kinds ; the first 
small round grains, resembling pollen-grains. These occupy principally the 
upper part of each sporange ; in the lower are found much larger bodies, which are 
oval, rather pointed, contracted in the middle, and at their apex have a conical 
projection. These are fertile spores, and as well as the former are contained in 
membranous bags (the thecaj). — A. 11.] Avery valuable paper by Mr. Valentine, 
upon “ The Germination and General Structure of Pilularia,” was read some years 
ago before the Linnean Society, and is to be found in their ‘ Transactions,’ for 1841, 
page 483. It gives an excellent account of the formation of the spores, 
and likewise of the germination, but he overlooked the process of fertilization. 
Speaking of the larger spore, he says : — “ The first external sign of germination 
is the appearance of four cells projecting through the apex. The enlarged cellular 
mass then distends the conical projection, and at length appears with four of its 
cells projecting beyond the general mass, and compressed into a quadrangular 
form.” [These cells are, in fact, the summit of an archegonium like that of 
Isoetes, &c., and the germinal vesicle lying at the base of this is fertilized by active 
spiral filaments, developed in and discharged from the small spores, as in the 
Lycopodiaceaj and Isoetaceae. — A. II.] “ These projecting cells soon harden, and ac- 
quire a reddish-brown hue — soon after which little fibrillae or rootlets begin to shoot 
from one side. They are simply articulated tubes, or elongated cells applied end 
to end, each produced from one of the cells of the genu (“ prothallium”). The 
germ (“ embryo”) now gradually points in two places, which are by no means 
fixed, but occur in various situations, according to the position of the sporule in 
respect to light. These two points gradually lengthen, and if dissected, each 
will be found to consist of a closed sheath, containing in one instance the leaf, 
in the other the root, in the form of a conical process like a finger in a glove. 
Besides this sheath which embraces the upper part of the root, there is au 
exceedingly delicate expansion which closely embraces the extremity of the root 
like a cap. After the leaf has grown to be many times the length of the sporule, 
or about two lines long, another leaf grows from the germ close to the first, to 
which it is in all respects similar ; and then a bud begins to be developed from 
some indefinite part of the germ, and like the leaves and root form within a sheath. 
This bud is covered by a peculiar kind of jointed hairs, whose attachments are 
lateral at a short distance from their bases.” 
Mr. Valentine then shows the origin and progress of the sporules within the 
