PLANTS JAVANIC^) RARI0RES. 567 



having a relation to two different trunks ; in other species, 

 in those particularly where the sori are most numerous, and 

 not confined to that branch, it is often difficult to deter- 

 mine the most important vein of the sorus ; and in Dip- 

 teris it is hardly practicable. 



From Dry n aria, and from those species of it especially in 

 which the principal vein of the sorus is distinctly marked, [4 

 the transition is easy to Polypodinm aureum, decumanum, 

 and a few other species having anastomosing veins, and in 

 which the sori are placed on the apices of two, or more 

 rarely three, connivent ultimate ramuli, included in an area 

 formed by the anastomosing secondary veins. But these 

 species, from the identity of habit, may be included in, or 

 appended to, a more extensive group, whose anastomosing 

 veins form areas or meshes, in each of which only one sorus 

 exists, and that terminating a single included branch. 

 This section, which may be named Phlebodium, and 

 whose species have either pinnate, deeply pinnatifid, or 

 more rarely simple fronds, appears to me strictly natural, 

 though it includes several species having the spurious in- 

 dusium of Pleopeltis, and at least one with an oval or even 

 oblong sorus. 



Next to Phlebodium in affinity, as well as in the ar- 

 rangement of the sori, may be placed a group, most of 

 whose species have simple fronds, and all of which are 

 natives of America. In this group, which may be distin- 

 guished by the subgeneric name Cyrtophlebium, the 

 primary parallel veins are connected by transverse 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. 

 In one species at least this branch reaches, and is united 

 with, the arched secondary vein above it ; and in a few 

 others it is entirely wanting. This arrangement in Cyrto- 

 phlebium produces two series of sori between each 

 primary vein, except in the lowest area, or that next the 



