ON GENERA AND SPECIES. 11 
termed the rachis, the primary rachis being a continuation 
of the foot-stalk (stipes); its first branches the secondary 
rachis, that is the rachis of pinnules. The pinne and pin- 
nules are as a rule alternate, but are also often opposite or 
nearly so, and they are either sessile or petiolate, and are 
either adhering and continuous with the rachis, or arti- 
culate with it, readily separating at the joint when mature, 
or earlier by dryness. In such the rachis remains long 
permanent, and even in some speeies of Nephrolepis the 
apex continues to grow, producing pinns. Their leafy 
part either tapers down to their base, such being termed 
sessile, or borne on a cylindrical or semi-cylindrical foot- 
stalk, but which is not special, being an integral part of 
the frond. 
They either grow erect or verge in various angles from ` 
the axis of development, some being nearly horizontal or 
bent downwards, their apex in such cases being ncm : 
viviparous, 
Fronds before evolution are densely covered with se, dye 
. termed ramente, or articulate hairs, these in most cases are 
early Szeen except at the base of the fronds. In Pleo- 
peltis, Lepecystis, and Ceterach, and some others, they are 
permanent, and specially characteristic. In some the 
. under side is densely covered with silvery or golden- 
coloured farina ; others are furnished with various hairs or 
is glands, which are generally viscid. Fronds are in most ` ` 
Ferns of two forms, sterile and fertile, but in the great 
majority the latter do not differ much from the former, = 
_ though they are in general narrower in all their parts. i : 
In several tribes they are normally of two distinct forms . 
3 (dimorphous), the sterile presenting the ordinary leafy ix 
. character, the fertile being specially contracted and thick- 
S ened, In some the contracted ieiunio Pu MM 
