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.]
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