Drvonian Plants from Ohio. 53 



of the scar is horseshoe-like, as in Protopieris, remains to be shown 

 by better specimens than any yet found, but it is evident that the 

 general character of the surface marking was essentially the same. 

 The most interesting feature in the specimen before us is the trunk, 

 which is composed of a vascular cylinder at the center, surrounded 

 by a mass of adventitious roots which form a large part of its diam- 

 eter. This structure is common enough in ferns of the present 

 day,* and has been recognized in many fossil forms (Psaronius) , 

 but never before in any fern of the Devonian age. 



Plate V., fig. 1, represents the exterior surface of the principal 

 portion of a trunk several feet in length. Here we see the leaf 

 scars distinctly indicated, and yet not sufficiently preserved to 

 exhibit all details 0/ their structure. It is evident that the trunk 

 has been partially decorticated, the spaces between the leaf scars 

 have been denuded and they themselves have been much injured by 

 maceration. The cortical integuments remain, however, and con- 

 ceal the interior mass of rootlets. Fibres are seen running into 

 this from some of the leaf scars that have been most decomposed. 



In fig. 2, a small portion of the lower part of the trunk is repre- 

 sented. Here the exterior coatings are entirely removed and we 

 see nothing but a bundle of adventitious rootlets. Owing to the 

 mode oi preservation, in limestone, the microscopic details of the 

 structure of the tissues are not preserved. 



In the cabinet of the Wesleyan University, at Delaware, is one 

 trunk apparently of this species which has a length of many feet , 

 this, like the specimen before us, was taken from quarries in the 

 Corniferous limestone at Delaware. 



Dadoxylon Newberryi, Dawson. 

 Plate VI., figs. 3, 3a, 3b. 



In the Huron shale on Huron River, in Erie County, about 

 Delaware, and at various places in the southern part of Ohio, 

 where this rock is exposed, masses of silicified coniferous wood are 

 frequently met with. They are portions of the trunks of trees 

 from a foot to two feet in diameter, often worn and rounded, 

 apparently floated masses which have ultimately become water- 

 soaked, have sunk to the bottom and been covered with the car- 

 bonaceous mud which now forms the great black shale of Central 

 Ohio. From the number of such masses of wood, it would seem 



* Dicks onia antarctica, from Tasmania, etc. 



