MOSSES. 73 
substance of the frond, or occurring free in the 
axils of the leaves, or immersed in special stalked 
receptacles. Besides this mode of reproduction, 
the scale-mosses are propagated by gemmae or 
little cellular nodules, which in one genus are pro- 
duced in elegant cups with a toothed margin 
growing on the upper surface of the frond; by 
innovations or new lobes growing out from the 
margins of the old fronds; by buds in the axils of 
leaves; and by confervoid branches sent out from 
the stem. The spores that are produced by the 
normal mode of reproduction have in most of the 
species a double coat, and germinate by protrud- 
ing pouch-like processes from which the new 
fronds or leafy stems arise. 
The Hepaticae or scale-mosses may be divided 
into two groups, consisting of those species in 
which the vegetation is frondose, that is, in which 
leaf and stem are confounded, and of those in 
which the vegetation is foliaceous, that is, in which 
leaves and stem are distinct. One genus of the 
frondose group called Riccia or crystal-wort floats 
on the surface of stagnant waters, and bears a 
superficial resemblance to the common duck-weed. 
The fronds, which are exceedingly delicate cellular 
leaf-like structures, are destitute of radicles when 
growing on the surface of ponds and ditches ; but 
if the water be removed by evaporation or drain- 
