602 FILICALES 
and leaf-form; but also upon the characters of the marginal sorus, and 
lastly upon the vascular system; for even the dendroid Dycksonias show 
a stelar system but little in advance of the solenostelic Dennstaedtias, 
allowance being made for the closer leaf-arrangement in their upright 
shoot. 
It is thus seen, not from one character alone but from several, that 
the Dennstaedtiinae take a transitional position between certain types 
of the simpler Gradatae and those Mixtae which have marginal or approxi- 
mately marginal sori. But lastly, the inequality of the lips of the indusium, 
and the obvious lopsidedness of the sorus, both in Dicksonza and in the 
‘Dennstaedtiinae, has its interest in relation to what is seen in some of 
the more advanced Ferns. The origin of the receptacle is still strictly 
marginal, but already there is a leaning towards the lower surface, and it 
will be seen that, in forms belonging to the Mixtae which appear to be 
related, this becomes more pronounced, till finally a superficial position 
of the sorus is fully attained. 
CYATHEAE. 
In all the Gradatae hitherto considered the sorus is of marginal origin, 
though in some of the most advanced there is a tendency towards the 
lower surface. But in the Cyatheae, in which the sorus is also basipetal, 
its position is superficial, being thus comparable with that of the Gleicheni- 
aceae or Marattiaceae. There is no comparative ground for referring this 
in the Cyatheae immediately to any transition from a marginal position: 
there is indeed good reason for believing that the superficial sorus was 
of very early occurrence, for it is exemplified in some of the most primitive 
types of Ferns. 
The Cyatheae as now limited include the dendroid genera A/sophila, 
Hemitelia, and Cyathea, though it will be seen that certain other genera 
of Ferns of smaller stature are probably related. In habit they are occasion- 
ally creeping (4. dlechnoides), but mostly of tree-like habit, the columnar 
stem being covered by the scars of the tufted leaves: these may be simple 
(C. sinuata), or singly pinnate (C. Brunonis), but usually repeatedly pinnate. 
Broad superficial scales are present generally, but hairs commonly accompany 
the sorus. Thorn-like outgrowths are not uncommon upon the surface, 
especially about the base of the petiole: these must be held as new 
formations, by enation from surfaces previously untenanted in descent: 
they show that such origin of new appendages existed among very early 
vascular Plants. Adventitious roots are numerous, and form a dense felt 
investing the lower part of the erect trunk to a thickness often far beyond 
its own bulk. 
The three genera named form a very natural group, separated from 
one another technically by the character of the indusium, which is absent 
in Alsophila, incomplete and scale-like in Hemdtelia, while in Cyathea it 
