THE CLASSIFICATION OF PLANTS 



2149 



do not, however, show any close correlation and a classification employing 

 the one feature cuts right across one employing the other. 



Apart from this, our ever-increasing knowledge of the fossil Pteridophyta 

 and the large number of early types described, which do not fit into the 

 groups of recent forms, make a basis of classification the more diflficult to 

 find. 



Classifications published before about 19 10 can therefore only be 

 considered as applying to present-day genera, for prior to that date our 

 knowledge of fossil Pteridophyta was too imperfect to exercise much in- 

 fluence upon classification. 



Historically we may, however, note that Linnaeus in his " Species 

 Plantarum " recognized some 200 species of Ferns and their allies, which 

 he divided among sixteen genera. After this the first general account of 

 the known Ferns was contributed by 

 O. Swartz, who in 1806 described 

 about 700 species in his " Synopsis 

 Filicum". Nineteenth-century writers 

 based their classification mainly on 

 soral characters,* but in 1836 Presl 

 made use of venation and vascular 

 structures in his classification, pub- 

 lished in his " Tentamen Pterido- 

 graphiae". Robert Brown in 1810 laid 

 down four of the families of living 

 Ferns and these were added to by later 

 writers, so that Mettenius in 1857-9 

 lists seven families out of the twelve 

 recognized by Christensen in 1938. 

 Between 1838 and 1842 \V. J. Hooker 

 (Fig. 2062) produced his great work, 

 the " Genera Filicum". This was 

 followed between 1844 and 1864 by 

 the " Species Filicum" and later by the 



" Synopsis Filicum " (1865-8), the latter being worked out after his death 

 by Baker. In this last work some 2,000 species were described. In 1905 6 

 Christensen published his " Index Filicum " with about 6,000 species of 

 Ferns and their allies. 



The classification of the whole of the Pteridophyta set out in Engler's 

 " Syllabus der Pflanzenfamilien " adopted the following system: 



F^IG. 2062. — Sir William lames Hooker. 



I . F ilk ales 



x. Filicales Leptosporangiatae 2. 



Eufilicineae 3. 



Hydropteridineae 



[3. Marattiales 



* Hooker laid down the condition that no character was admissible in the classification 

 of Ferns which could not be observed with a hand lens on an herbarium specimen! 



v. Ophioglossales 

 Sph en ophy Hales 

 Equisetales 

 y.. Euequisetales 

 p. Calamariales 



