28 BRITISH FERNS. 
the recommendation of proof. All our Floras tell 
a different tale: no links have been supplied to 
compensate for those that have perished. Whoever 
reads Nature aright will readily understand the diffi 
culties under which those are labouring who en- 
deavour to build up a system with such scanty 
materials. For my own arrangement I claim no 
merit: I should be most unwilling to assert its 
superiority over others, 
Plants are grouped into four Provinces called 
Exogens, Endogens, Acrogens and Thallogens: the 
first and second of these Provinces consist entirely 
of flowering plants; the third and fourth, of those 
which are without flowers. Acrogens, though without 
flowers, have distinct roots, stems and leaves, and 
the two halves of the latter are generally symme- 
trical. Such are Ferns, and these characters at once 
distinguish them from Sea-weeds, Lichens or Fungi, 
which are properly designated “Thallogens.” Acros 
gens are again divided by the structure of their 
leaves; they are either what botanists term vascular, 
that is, composed of bundles of vessels, or cellular, 
which means composed of simple cells; this division 
