660 GENERA OF FERNS. 
and which often present different appearances, according to 
age or the part of the plant from which the specimen was 
taken. From my own observation, I am satisfied that au- 
thors, when characterizing presumed new species (of ferns 
generally), do not make due allowance for the variations con- 
sequent upon age, and the influence of local causes connected 
with the place of growth. 
The species constituting Cyathee (with the genus Dick- 
sonia) are truly the giants of the fern race, having erect, 
arboreous, usually hollow trunks (rhizoma), often attaining 
the height of fifty or more feet, and bearing a crown o 
large, generally decompound fronds, each sometimes nearly 
20 feet in length. Their stipites, or bases, being either 
permanent and becoming indurated, form part of the solid 
structure of the trunk; or they are deciduous, and separate 
from the trunk by a distinct articulation, which is perma- 
nently indicated by oblong rhomboid marks or scars, dis- 
posed in a spiral series on the trunk. With the exception of 
the genus Hemitelia, the venation of this tribe is direct and 
free, with the sori situated between the base and apex, or on, 
or near, the axis of division of forked veins; the position of 
the sori distinguishing Cyathee from the preceding tribe 
Dicksoniee, where the sori are always terminal and marginal. 
The circumstance of an apparent obliquity of the ring of 
the sporangia of Cyathee, has induced several authors to 
adopt it as an important structure for divisional ment. 
I have already stated, under Trichomanes, and also att. 31 
in Hooker and Bauer’s Genera Filicum, that my opinion of the 
cause of the apparent obliquity of the ring does not allow 
me to consider it normally different from true Polypodiacee. 
Presl has used it as the technical character, for his first Order 
of Aunulate Ferns, which he calls *Helicogyrate," and which 
is constituted of Cyathee, and the species composing a sub- 
sequent division of this arrangement, the Gleicheniacee of 
Brown; between which and Cyathee I see no direct 
affinity, except in the somewhat analogous structure of the 
sporangia and direction of the ring. According to my view, 
