56 MESOZOIC FLORAS OF UNITED STATES. 



when the remaining pinnules are entire. The degree of union of the pin- 

 nules depends upon their position, they being more united and passing 

 into lobes in terminal parts. In the opposite direction and lower in the 

 compound pinnae they are more incised. In passing to lower portions the 

 entire pinnules pass through those with undulate margins into those with 

 dentate and lobed margins, and finally into ultimate pinnae, the lobes 

 becoming pinnules. The tips of the pinnules range from acute forms in 

 the entire ones to subacute or obtuse ones in the incised pinnules. The 

 leaf substance must have been thick and leather-like, with an epidermis 

 that was very dense and durable, for much of the plant matter is often 

 preserved, giving a shining film on the rock. The nerves are those of 

 Cladophlebis. In the entire pinnules there is a midnerve set on obliquely. 

 This splits up into branches toward the end. One or more branches may 

 be given off very obliqi^ely from the sides of the midnerve. These may 

 be forked if they are basal nerves, but are mostly single. 



The sori, in proportion to the size* of the pinnules and lobes, are 

 very large. Many of the specimens present the lower surface of the 

 foliage uppermost, so that the sori are well shown, and in many cases 

 they are remarkably well preserved. They are placed within the margin 

 and are attached to the end of one of the lateral nerves. In the case 

 of the entire pinnules there is only one sorus, and this is on the end of 

 the lateral nerve given off from the base of the midnerve on its upper 

 side. The sorus is so large that it covers most of the surface of the 

 anterior base of the pinnule. The pinnules with dentate or lobed mar- 

 gins have a sorus for each tooth or lobe placed on the ends of lateral 

 nerves and covering the anterior portion of the tooth or lobe. Often 

 nothing but these large sori can be seen in such pinnules, and by their 

 position they outline the form of the pinnule. 



The sori are covered by a thick durable indusium, which is appar- 

 ently inserted under them. The sori stand out strongly convex and 

 leave deep pits in the rock. They are globular in form, with a slight 

 elongation. Owing to distortion they vary a good deal in their present 

 form. When, however, the specimens present the upper surface upper- 

 most, so that the sori must be seen through the lamina, they appear 

 much smaller and are punctiform elevations. 



The fructification as made out is near enough to that of Dicksonia 

 to justify placing the plant in that group. 



