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
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