ON GENERA AND SPECIES. 23 
genera under two divisions. The first, which he terms 
— “ Nudis” consists of six genera, characterised by the sori 
— being naked, that is destitute of indusium, by some termed 
gymnosorus ; this division contains 167 species. The other 
genera being furnished with an indusium he terms “ In- 
dusiates,” which comprehends 467 species. These two ` 
divisions embrace all Ferns which have their sporangia 
—. furnished with a vertical ring; as also the genera Hymen- 
- ophyllum and Trichomanes, in which the ring is horizontal. 
The next systematic arrangement of Ferns appeszed in 
1810, in the fifth volume of the * Species Plantarum " of 
Willdenow, wherein 1,010 species of circinate Ferns are 2555 
described, comprehended under forty-one genera, being an a 
addition of five new genera since Swartz. Three of these ` 
. new genera are founded on species retained by Swartz in 
^: Linnean genera, the other two (Polybotrya and Pleopeltis), are 
each founded on a single species, for which the authority « of 
.. Humboldt and Bonpland is given, As the characters upon ` 
. which Willdenow founded his genera do not bring forward ` 
any striking new feature of structure, beyond certain modi- 
. fications in the nature of the indusia and contraction of the 
. fertile frond, I do not deem it necessary to speak further of 
them in this place. The first pictorial work at that period 
. was the “Kryptogamische Gewiichse ” (plants), by Pro- 
fessor Schkuhr, of Wurtemburg, published in 1809 ; it iba 
quarto volume containing 196 finely executed coloured 
plates representing 263 species of circinate Ferns, and 
accompanied by 212 pages of descriptive text. ‘The Am. - 
portance of this work is manifested by the fact that all ` 
£ ing pteridologists quote the figures as evidence in 
the identification of species.  - : 
The above were followed by special works and eni 
ous. e in jounal on Zeng, the ee writers 
