HETERANGIUM 411 



previously unknown. She permits me to quote the 

 following brief statement of her results : " Recently in 

 a series of nineteen transverse sections through a single 

 stem of H. Grievii, roots were found emerging from the 

 stele and branching in the cortex, which was locally 

 much thickened. In some sections these roots were 

 cut transversely, and proved to be diarch or triarch. No 

 exodermis could be distinguished from the rest of the 

 cortex, as in Lyginodendron'.' In the case of the Coal- 

 measure species, H. Lomaxii, there is some evidence 

 that the roots were tetrarch, but proof of continuity is 

 not yet established. 



4. Heterangium tiliaeoides. — The other forms which 

 have been referred to the genus Heterangium agree 

 in essentials with H. Grievii, but there is one which 

 deserves special notice, on account of the astonishing 

 perfection with which its tissues are preserved. This 

 is the Heterangium tiliaeoides of Williamson, first 

 described by that author in 1887, 1 from specimens 

 found in the Lower Coal-measures of Halifax. The 

 general structure is like that in the species already 

 described, and here also the entire interior of the stele 

 is occupied by groups of tracheides interspersed with 

 conjunctive parenchyma. The primary, mesarch xylem- 

 strands at the periphery of the central wood, are, 

 however, much more distinct in the Halifax species, 

 and at once strike the eye as definite bundles, separated 

 from one another by bands of conjunctive tissue. The 



1 "Organisation of Fossil Plants of the Coal- Measures,'' Part xiii., 

 Phil. Trans. Roy. Sac. B, vol. 178, 1887. See also Williamson and 

 Scott, "Further Observations," etc., Part iii., Phil. Trans. B, vol. 186, 

 1895. 



