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 appeared in 

 1810, in the fifth volume of the " Species Plantarum " of 

 Willdenow, wherein 1,010 species of circinate Ferns are 

 described, comprehended under forty-one genera, being an 

 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 farther of 

 them in this place. The first pictorial work at that period 

 was the " Kryptogamische Gewachse " (plants), by Pro- 

 fessor Schkuhr, of Wurtemburg, published in 1809 ; it is a 

 quarto volume containing 196 finely executed coloured 

 plates representing 263 species of circinate Ferns, and 

 accompanied by 212 pages of descriptive text. The im- 

 portance of this work is manifested by the fact that all 

 succeeding pteridologists quote the figures as evidence in 

 the identification of species. 



The above were followed by special works and miscel- 

 laneous writings in journals on Ferns, the principal writers 



