12 ON GENERA AND SPECIES. 



(rachiform), in others they are involute, in the form of a 

 pod or siliqua (siliquiform) in others plain, the under 

 surface being densely occupied with sporangia ; in some, 

 the lower portion of the frond is sterile, while the upper 

 portion is contracted and fertile. 



The duration of fronds is variable, some remaining per- 

 manent for several years, but the greater majority, espe- 

 cially those in temperate and cold climates, develope and 

 come to maturity in one year. 



It is, however, otherwise with the genera GleicJienia, Lygo- 

 dium, and Salpichlcena ; in the first the fronds are dicJio- 

 tomous ; and from the axis of the forks are successively 

 produced other dichotomous branches, and the fronds thus 

 continue long permanent. 



As regards Lygodium, the fronds so called continue to 

 lengthen and branch (indefinite), rambling over bushes or 

 climbing the tops of lofty trees ; such is also the case with 

 the blechnoid Fern Salpichlcena. The permanent nature 

 of these climbing fronds (?) may be considered analogous 

 to climbing flowering plants, such as Clematis; to these 

 peculiar growing Ferns I apply the term Pterampelids. 



VENATION. 



The vascular structure of Ferns consists of cords of 

 indurated tissue termed scalariform, which branches from 

 the base of the previous frond into the nascent bud of the 

 forthcoming frond, and lengthen upwards with the growth 

 of the frond. It consists of one, two, or more cylindrical, 

 flat, or channeled cords, which, on reaching the leafy part 

 of the frond, divide and ramify through all its parts, the ul- 

 timate ramifications ending in the leafy part (lamina), being 



