496 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



The sterile fronds. — The leaves of Gigantopteris, as commonly 

 gathered, in apical or interdichotomal fragments, resemble nothing 

 so much as portions of the broad lanceolate or linear-lanceolate 

 leaves of some dicotyledonous genus with rather close, open, and 

 well-defuied secondary nerves. Only when the nervation is examined 

 more closely or the dichotomy of the leaf is noted is the real nature 

 of the plant suspected. The specific name, nicotiansefolia, given by 

 Schenk to the Chinese form is therefore descriptively appropriate. 

 When larger pieces are discovered or put together the fronds of the 

 Texas plant are found to be broadly ribbonhke, sympodially (?) fork- 

 ing (pis. 43, 44, and 45) rather distantly, and slightly narrowed at 

 the points of bifurcation, as shown in plate 43, so that the segments 

 have a linear-lanceolate to lanceolate form. The angle of dichotomy 

 is rather wide, generally about 60°. The lamina, which is not very 

 thick, is generally strongly convex on the ventral surface between 

 the secondary nerves; it is united for its whole width above each 

 dichotomy, and is either abruptly terminated below, or gradually 

 narrowed, while becommg lobately-incised or modified, at the base of 

 the frond, as indicated in plate 46, figure 3, and plate 48, figure 5. 



The border of the leaf is sinuate. As seen in fossils like that 

 shown on the right in plate 45, it may be round-convex about the 

 end of each secondary nerve; in other examples it is concave opposite 

 the ends of the same nerves, as shown in plate 44 and plate 47, 

 figure 1, while in still others, including the very young example, 

 plate 46, figure 3, both phases are found. It is notable, however, 

 that in the basal portions of the frond, in which lobation may be 

 found, the margins are naturally convex opposite each secondary 

 nerve, whose region of distribution corresponds to a lobe, and is in 

 some specimens a well-defined lobe. The varying sinuosity of the 

 margin is probably due to partial maceration and shrinkage in 

 the lamina; convexity of outline opposite the secondary nerves is 

 presumably the normal condition. The nervation appears to have 

 offered greater rigidity and support for the lamina opposite the 

 sutural nerves in the large leaves than appears to have been afforded 

 at the ends of the secondary nerves themselves. 



The nervation of Oigantopteris is an anomalous as well as very 

 striking chai'acteristic of the plant. As may be noted in the frag- 

 ments shown in plates 43, 44, 45, and 47, figure 1, or even in the 

 very young frond seen in plate 46, figure 3, the secondary nerves 

 emerge, equidistant and parallel, at a conspicuously wide angle from 

 the very broad, deeply depressed and irregularly lineate median 

 nerve of the segment, and pass, ventrally depressed, nearly straight 

 or with a slight outward turn toward the margin. They are a little 

 decurrent at the base, and taper slightly upward to near the border 

 where they become rapidly effaced like those of Alethopterls, as 



