376 STUDIES IN FOSSIL BOTANY 



xylem. In the specimen figured the preservation is 

 surprisingly perfect, every cell of the phloem being 

 present. The convex side of the bundle is directed 

 towards the lower surface of the petiole. The structure 

 of the wood is like that of the primary bundles in the 

 stem ; the spiral elements occur in several groups in 

 each bundle, and are placed in the interior of the xylem, 

 towards its lower surface. In the specimen shown in 

 Fig. 139 there are probably three protoxylem-groups, 

 one near the bend of the V, and one towards the end 

 of each arm. 



The inner cortex contains bands of sclerotic tissue, 

 like those in the stem, but more distinctly transverse, 

 and the outer cortex is here also a network of fibrous 

 strands, enclosing parenchyma in their meshes. The 

 curious blunt spines, described above as occurring on 

 the stem, are just as abundant on the leaf, where they 

 are present on all parts of the petiole and rachis, and 

 even extend onto the leaflets (see Fig. 140). 



In some cases the minute structure of the leaflet is 

 wonderfully well preserved (see Fig. 140) ; below the 

 epidermis of the upper surface we can distinguish a 

 hypodermal layer, beneath which again is well-char- 

 acterised palisade -parenchyma. Towards the lower 

 surface the mesophyll has a laxer structure, constituting 

 the spongy parenchyma ; occasionally, traces of stomata 

 have been detected in the lower epidermis. The fine 

 vascular bundles traversing the lamina are enclosed in 

 distinct sheaths, and appear to have been collateral in 

 structure, as is so often the case in the ultimate ramifica- 

 tions of the bundles in the leaves of recent Ferns. The 

 whole structure is altogether comparable to that of a 



