216 Bibliographical Notices, 



now consisting of about three hundred species, and observes, that 

 '• 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 struc- 

 ture, or the various ramifications of the bundles of vessels, or veins 

 of the frond, combined with the relation of the sori to their trunks 

 or branches." This principle of subdivision in Ferns, first employed 

 by Mr. Brown himself in the characters of various genera in his 

 * Prodromus Floras Novas Hollandise,' has since been adopted with 

 considerable advantage by several writers on the subject. The sub- 

 genus in question agrees with Drynaria of M. Bory in the position 

 of its sori at the point of confluence of several veins, but differs from 

 it and from all other groups of Polypodium in the dichotomous rami- 

 fication of its primary veins, which is necessarily connected with the 

 peculiar division of the frond, and forms, therefore, a character of at 

 least equal importance with those on which several groups, of sup- 

 posed generic value, have been founded. Setting aside this peculiar 

 ramification, there remains no sufficient character to distinguish Di- 

 pteris from Drynaria ; and Drynaria itself can only be separated from 

 a more extensive section comprehending Polypodium plymatodes, &c, 

 by the presence of sterile fronds. From this section Mr. Brown 

 passes to the consideration of an extensive group, also having ana- 

 stomosing veins, but in which the sori are seated on the apices of one, 

 or occasionally of two or three ultimate ramuli, included in an area, 

 formed by the anastomosing secondary veins. To this section he 

 gives the subgeneric name of Phlebodium ; and next in affinity to it 

 he places a group, most of whose species have simple fronds, and all 

 of which are natives of America, to which he assigns the name of 

 Cyrtophlebium, its primary parallel veins being " connected by trans- 

 verse arched branches, from the convex upper side of which generally 

 three (and never more than three) upright parallel simple veins 

 arise, terminating within the area included between the proximate 

 transverse arched branches ; of these simple tertiary ramuli the two 

 lateral are soriferous, generally below the apex, the middle branch 

 being always sterile." An analogous arrangement, but with some 

 modifications, exists in the real species of Cyclophorus, none of which 

 are natives of America. Mr. Brown next proceeds to notice an ex- 

 tensive and strictly natural group or subgenus, the Lastrea of M. 

 Boiy, the closest affinity of which he states to be " not to any group 

 of Polypodium, but to that section of Gymnogramma, the division of 

 whose fronds, and the disposition of veins, are exactly similar, and 

 in which the sori form very short lines of like origin." The distinc- 



