PLANTS JAVANIC.E RARIORES. 565 



distinct section or subgenus of Polypodium, to which they 

 must be referred, while the characters of that genus consist 

 merely in its round sori, and absence of true indusium. But 

 in adding two species, having so singular a habit, to a genus 

 already too extensive, and including so many different 

 forms, it must be evident that the present sources of 

 generic distinction in this Natural Family are very insuffi- 

 cient for its satisfactory analysis. 



The number of Ferns at present known, including un- 

 published species existing in collections, may be stated at 

 upwards of 1800. The Family has been subdivided into 

 five primary groups. These groups are strictly natural ; 

 they are not, however, of equal value as to the importance 

 of their characters, and they are extremely unequal in 

 extent ; the great mass belonging to that called Polypo- 

 diacese, which has been divided into upwards of fifty 

 genera, and contains about 1600 species. Of this number 

 nearly one half, or 800, belong to five genera, namely, 

 Polypodium, Aspidium, Nephrodium, Asplenium, and 

 Pteris, as they are at present constituted, Polypodium alone 

 consisting of about 300 species. The extent of Polypo- 

 dium, therefore, renders its subdivision into natural sections 

 or subgenera absolutely necessary. 



For such subdivision, not in Polypodium only, but in 

 other extensive genera of Ferns the most obvious, as well 

 as the most advantageous source of character seems to be 

 the modifications of vascular structure, or the various rami- 

 fications of the bundles of vessels, or veins of the frond, com- 

 bined with the relation of the sori to their trunks or branches. 



On this subject many important observations have been 

 made, and subdivisions founded on them proposed by 

 several writers, especially MM. Bory, Gaudichaud, Kaul- 

 fuss, Ad. Brongniart, and Blume. I may add, that I have 

 at a still earlier period 1 introduced the ramification and 

 relation of sori to veins into the definitions of several 

 genera, in which these characters had not been before em- 

 ployed, and have more recently, 2 in treating of Matonia, 

 pointed out a natural and extensive group in Polypodium, 



1 ['Prod, Fl. Nov. Holl.; i, p. 156-8.] 2 [Ante, pp. 542-3.] 



