FOSSIL PLANTS OF THE CAEBONIFEKOUS SYSTEM. 735 



Stigmaria {eTiyfi^a, a mark or impression) is a fossil genus, the 

 species of which abound in the Coal-measures. They occur generally 

 in the bed called the Underclay. Stigmaria ficoides (fig. 914) is the 

 common species. It sends forth grooved and pitted branches, which 

 divide dichotomously, and extend 20 to 30 feet. Slender processes 

 are given off, which appear to have been hollow (fig. 914). These 

 processes (called fistular roots) form an entangled mass traversing the 



Fig. 915. 



argillaceous lower bed in every direction. In Stigmarias three tissues 

 are met with, — vascular tissue forming the inner part of the cylinder, 

 ligneous forming the wood, and cellular tissue forming a broad cortical 

 zone, as well as the central portion or pith. Stigmaria is apj)arently 

 a thick rhizome, having a large medulla, surrounded by a cylinder 

 of scalariform vessels, and with a mass of cortical parenchyma sur- 

 rounding the whole. Kootlets proceed from the pits on the sides of 

 the rhizome, each containing a small bundle of scalariform vessels 

 having its origin in the vascular cylinder. In the structure of its 

 stem it agrees, according to some, with Oycads, and with certain 

 fleshy Euphorbiacese and Oactacese. According to Williamson, Stig- 

 maria has a pith surrounded by a thick woody zone, containing two 

 distinct sets of primary and secondary medullary rays, the former 

 going direct to the bark. In what are called decorticated stems of the 

 Lepidodendroid plants, the more central axial portion (medulla, wood, 

 and thin layers of inner bark) have disappeared through decay; the bast 



Fig. 914. Stigmaria flooides ; a branch giving off fistular leaves, wliioh traverse the 

 underclay in all directions. Fig. 915. SigiUaria pachyderma ; showing fluting of the 



stem, and the soars of the leaves. 



