PRINCIPLES OF CLASSIFICATION. 35 



tion they can scarcely be ; and we may rather con- 

 sider their nature and use as undetermined. They 

 perhaps differ little from the woolliness 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 

 subsequently 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 mu- 

 table, figure than in any others. Ferns want the 

 above-mentioned jointed fibres of Mosses in germi- 

 nation. 



9 1 . From what has been said (90) it appears that the 

 old appellation of Acotyledones may commodiously 

 remain with Cryptogamic vegetables in general (71), 

 though the form of their Embryo, and mode of 

 germination, are, in some of this tribe, only pre- 

 sumed 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, respecting 

 the point in question, was incomplete, and he has 

 candidly owned his difficulties. Most of the plants, 

 on being better understood, prove either dicotyle- 



