20 THE OLDER MESOZOIC FLORA OF VIRGINIA. 



do not appear on the margins of the leaf. While the upper part and 

 termination of the leaves usually show a very regular curve in their mar- 

 gins, we find towards the middle and lower portions a more or less distinct 

 undulation, which often becomes very marked towards the base. The fronds 

 all narrow gradually towards the base and the lamina rather suddenly 

 ceases, one-half being usually more prolonged than the other. The midrib 

 is prolonged for some distance into a rachis that supported the frond, which 

 latter is of course single. The frond seems to have been thin when we con- 

 sider its great size, but the epidermis was strong and durable. It may often 

 be stripped off from the fine-grained shale like thin paper. This epidermal 

 tissue has, in the Hanover Area, formed a local deposit of coal 4 or 5 inches 

 thick. It seems that here immense numbers of the leaves of this plant were 

 accumulated in an eddy of the water, and being heaped one over the other, 

 give us a coal composed of epidermal tissue mainly. The epidermis 

 becomes greatly thickened near and over the midrib, so that the insertions 

 of the lateral nerves are mostly hidden, and the midrib appears to be much 

 wider than it really is. When this portion of the epidermis is removed by 

 maceration, as it often is, the true nature of the lateral nerves, their inser- 

 tion, and the true width of the midrib are disclosed. All of these points 

 cannot be made out when the epidermis covers the fossil. Professor Rogers 

 seems to have made his stud}' of the plant from specimens which retain the 

 epidermis, and hence he failed to note some of the characters of the fossil. 

 The midrib was evidently fleshy in nature, and had but comparatively 

 few woody bundles. It owed much of its strength and rigidity to the strong, 

 thick epidermis that covered this portion of the plant. It is as flat as a 

 ribbon, and in those plants which are freed from the epidermis it is seen to 

 be composed of but few nerve-bundles, which appear to have been immersed 

 in a rather soft and succulent material, which, readily yielding to pressure, 

 became perfectly flat on the thinly-laminated and fine-grained shale. When 

 the thick epidermis over and near the midrib is in place it conceals the 

 insertion of the lateral nerves. These, then, often appear to issue as single 

 nerves, when, if the epidermis be stripped off, they are seen to fork very 

 commonly close to their insertion. The striations seen on the midrib are 

 the nerve-bundles showing through the epidermis. Seen on well-preserved 



