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 pinnae 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 species of Nephrolepis the 

 apex continues to grow, producing pinnae. 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 generally 

 viviparous. 



Fronds before evolution are densely covered with scales, 

 termed ramentce, or articulate hairs, these in most cases are 

 early deciduous, except at the base of the fronds. In Pleo- 

 peltis, Lepecystis, and Geterach, and some others, they are 

 permanent, and specially characteristic. In some the 

 under side is densely covered with silvery or golden- 

 colo tired farina ; others are furnished with various hairs or 

 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. 

 In several tribes they are normally of two distinct forms 

 (dimorphous), the sterile presenting the ordinary leafy 

 character, the fertile being specially contracted and thick- 

 ened. In some the contracted segments are very narrow 



