ACROGENS. 271 
force. This consists of a single fibre, or two twisted spirally 
in different directions so as to cross each other, and is con- 
tained within a very delicate transparent perishable tube.” This 
order contains the—I. Marchantiacea, or Liverworts, which root on 
the ground, on walls, rocks, and damp places; II. Ricciacee, float- 
ing plants, rooting on the ground, their fructification immersed in 
the frond. III. Anthoceratew, annuals with fleshy or membranous 
fronds, spore cases raised on a pedicel, two or three inches long, 
with a free central columella. IV. Jungermaniacee, frondose or 
foliaceous plants, spore cases opening with four valves, spores 
mixed with elaters. ; 
The structure of the plants, some of them of microscopic minute- 
ness, is singularly interesting. They are furnished with leaves, 
arranged over a distinct axis of growth; and their reproductive 
organs are of two kinds, the most general being the urn sporangium’ 
or theca, in which the spores or seeds are generated. If examined 
in the season of growth, it will be observed that some of the axils 
of the leaves contain clusters of articulated filaments, swollen at 
the base, some of them being larger than the others. After a while 
this body is found to have an exterior membranous coating, which 
Separates from the base in a cup-like form ; this is the young urn, 
which gradually acquires a stalk called the seta, upon which it is 
raised above the leaves carrying the other membrane upward on its 
. Point, covered, when full grown, with a cap, called its ca/yptia. 
the urn is closed by a lid, its operculum, and contains the spores 
ma cavity surrounding central column, or columella. Its rim is 
bordered by a double set of teeth, like jointed processes, called the 
beristoma. 
A second set of organs called Antheridia are observed, which - 
also form clusters in the axils of the leaves; they are membranous 
cylindrical jointed, or jointless, bodies, irregularly opening out at 
the Point and discharging a mucous turbid fluid. Now the func- 
tion of these two sets of organs has long been a subject of dispute. 
The discovery of the two kinds of organs, the Antheridia and 
Pistillidia, in the Mosses and Hepaticess, and the analogous spiral 
"ments in the Characee were supposed to indicate a sexual orga- _ 
. nisation. Professor von Mohl pointed out the analogy between the 
clopment of the spores of the Cryptogamia or Thallogens and 
