INTRODUCTION. 45 
or nearly so, and bursting vertically ; while the fronds are rigid and 
opaque, and are usually dichotomously-branched. 
(5) Trichomaninee, in which the ring resembles that of the 
Gleicheninece, but the spore-cases are lenticular, numerous, clustered | 
on an exserted receptacle, which is, in fact, a prolongation of the 
vein beyond the ordinary margin of the frond, so that the sori 
become extrorse-marginal, or projected outwards as well as opening 
outwardly; while the fronds are pellucid-membranaceous. 
(6) Schizeinec, in which the ring is either horizontal or transverse, 
but situated quite at the apex of the oval spore-case, which is, in 
consequence, said to be radiate-striate at the apex; the spore-case 
is also sometimes resupinate, or turned upside down, so that the 
true apex is below. 
(7) Ceratopteridinec, consisting of one or two, perhaps only a single 
aquatic species, in which the spore-cases are sometimes furnished 
with a very rudimentary ring, reduced, as in Osmundinec, to a few 
parallel strie, sometimes furnished with a very broad and more 
lengthened ring. In this little group, the spores themselves furnish 
an excellent supplementary characteristic, being bluntly triangular, 
marked with three series of concentric lines. 
(8) Osmundinee, which is distinguished from the rest by having 
its spore-cases two-valved, bursting vertically at the apex; the ring, 
moreover, is very rudimentary indeed, being reduced to a few 
parallel vertical stri (parallel elongated cells of the tissue) on one 
side near the apex of the spore-case. In all the preceding tribes, 
the spore-cases are not valvate, and consequently, when they open 
for the liberation of the spores, they burst partially or irregularly, 
and do not split at the top in two equal divisions, as occurs in the 
Osmundinee. 

