132 



FILICES. 



speaking, of no value ; the contrary is the case when they are petrified and 

 it is possible to determine their inner structure. All such leaf-stalks are 

 usually comprehended under the name Rachiopteridae. The same may be 

 said of the stems, which form a large portion of the fern-remains preserved 

 to us ; they, like the Rachiopteridae, can only in the very rarest instances be 

 referred with certainty to particular given leaves. It is true that we not 

 unfrequently find the two kinds of organs spoken of in the literature as 

 belonging to one another, but statements of this kind rest, except in a few 

 cases l , on conclusions frpm the fact that the parts occur together in the 

 strata, and of such conclusions we have already said what is needful in the 

 introductory chapter. 



Fern-leaves furnish perhaps the one instance in which systematic 

 botany has received a direct impulse from palaeophytology. Our entire 

 fern-system is founded on the nature of the fructifications, and these are 

 not often to be seen on the fossil leaves, and when present are usually 

 indifferently preserved. When then Brongniart 2 addressed himself to the 

 task of classifying all known fossil fern-leaves, the number of which was 

 very considerable even then, and perceived that the few fructifications with 

 which he was acquainted could be of no use to him, he seized with his 

 wonted energy and precision on the only expedient which presented itself, 

 namely, the course of the nerves ; and upon this character, to which little 

 attention had been paid up to that time, he founded a classification of fossil 

 Ferns which is confessedly artificial and not in accordance with that of recent 

 forms. Brongniart's method was afterwards applied, as we know, by Presl 3 

 especially and by A. Braun 4 to living species, and in the hands of 

 Mettenius 5 above all others it proved to be extremely fruitful as a subor- 

 dinate principle of division. Goppert 6 , who had in the meantime become 

 acquainted with a number of fossil fructifications, thereupon attempted to 

 combine Brongniart's classification with that of the botanists, but the 

 attempt was an entire failure and he himself subsequently abandoned it ; 

 his genera defined and named, some simply after Brongniart, others accord- 

 ing to the fructifications, others again from their resemblance to recent 

 genera, run in confusion one into another, and no connected view of the 

 whole system is possible since the main principles of division are incom- 

 mensurable. Systematists have since then been repeatedly guilty of this 

 fault in logic ; Schimper's 7 account of these forms especially suffers from 

 the same cause. 



It was soon felt to be necessary to break up the great form-groups 

 which Brongniart had founded on the course of the nerves, into further 

 divisions. Systematists have often employed for this purpose the form and 



1 Schimper (3), t. 40, and Sternberg, Graf von (1), Heft 5-8, t. 59. ' Brongniart (1). 



3 Presl (1\ * A. Braun (1). s Mettenius (1). Goppert (2). 7 Schimper (1). 



