PRINCIPLES OF CLASSIFICATION. 35 



be ; and we may rather consider their nature and 

 use as undetermined. They perhaps differ little 

 from the tvoolliness so common on the Stem of 

 these plants in an advanced state. Filices, Ferns, 

 (77) differ somewhat from Mosses in having a 

 membranous and flat expansion of the Embryo, 

 sometimes fixed by the centre. Still this part 

 may be considered as simple, and what are sub- 

 sequently produced, however shapeless, are doubt- 

 less of the nature of Leaves, or Fronds (24), which 

 in these plants are of a more Proteus-like, or 

 mutable, figure than in any others. Ferns want 

 the above-mentioned jointed fibres of Mosses in 

 germination. 



91. From what has been said (90) it appears that 

 the old appellation of Acotyledones may commo- 

 diously remain with Cryptogamic vegetables in- 

 general (71), though the form of their Embryo, and 

 mode of germination, are, in some of this tribe, 

 only presumed from analogy. Those with which 

 we are acquainted are certainly destitute of any 

 Cotyledon, and of any separate Albumen. 



92. Jussieu, however, ranks under this denomination 

 an Order termed Naiades, consisting of aquatic 

 plants, with perfect, not cryptogamic, fructifica- 

 tion. Of many of these his knowledge, respect- 

 ing the point in question, was incomplete, and he 

 has candidly owned his difficulties. Most of the 

 plants, on being better understood, prove either di- 



d 2 



