SCALE MOSSES 247 
thickened. By the expansive force of these elaters 
the sporophyte is ruptured somewhat stellately, and the 
spores are forced out. When the spores germinate they 
give rise directly to the gametophyte generation. 
433. The Scale mosses (Order JUNGERMANNIALES) 
are the highest of the Liverworts, and also the most 
numerous in species. In-the lower family (Metz- 
geriaceae) the gametophyte is usually a thal- 
lus as in the liverworts already described, 
butin the higher family (Jungermanniaceae) 
it is a creeping, leafy stem. In the first 
family we find all gradations from the en- 5, 453 _ 
tire margined thallus to those with more and- }retsgeria, and 
more pronounced lateral lobing, and finally 
to those in which the lobes have become distinct leaves 
on a rounded stem. The leaves of Scale mosses are 
but one cell thick and are not ribbed. 
434. The antherids and archegones are borne dorsally 
or subterminally and are much like those already 
described. The sporophyte develops a slender stalk 
which carries up the enlarged spore case, and the latter 
when the spores are mature splits vertically into four 
segments and permits the escape of spores and elaters. 
When the spores germinate they may develop directly 
such adult gametophytes as are described above, while 
in the higher forms the gametophyte is first a filamentous 
or thalloid structure (‘‘protonema’’) from which the 
adult gametophyte subsequently buds out. 
435. Many Scale mosses reproduce by means of brood 
masses much like those of Marchantia, of even simple, 
single-celled structures (brood cells). 
436. Scale mosses have no stomata on either gameto- 
phytes or sporophytes. 
