The Fossil Plants of the Coal Measures. 63 



Outermost Cortex. 



Transverse . 



D.— p. 398, Fig. 35. See C.N. 1244k." 

 Longitudinal. 



D. p. 398. Fig. 32k", C.N. 1278k". 



Young Twigs. 



Transverse. 



D. — p. 402, Fig. 46, C.N. 1244, 1280, 1283, 1295, and 1296. 

 Longitudinal. 



D. — p. 4C2, Fig. 47. See numerous sections in C.N. 1287 and in C.N. 

 1296*. 



HETERANGIUM TILIjEOIDES. Will. 



This plant approaches so closely to H. Grievii, not only in 

 the general type of its structure, but even in many of the 

 details of its organisation, that I see no reasonable grounds 

 for placing them in separate typical groups. At the same 

 time, as I have shown in my Memoir XIX., notwithstanding 

 its typical resemblances to H. Grievii, and though the differ- 

 ences between the two are those of detail, and not of type, 

 the beautiful structures of H. Tiliceoides show a distinct 

 advance to a higher order of exogenous organisation than 

 we find in the former plant. So far as its central vasculo- 

 medullary axis is concerned, it is a true Heterangium in 

 every detail characteristic of the genus ; but when we turn 

 to the aspects of its secondary xylem, and its investments 

 of highly developed Phloem, we discover the differences 

 between the two forms. This is important. Lyginodendron, 

 now clearly proved to be a true fern, carries inseparably 

 along with it Heterangium Grievii, and in like manner the 

 latter cannot be disjoined from H. Tiliceoides. If all this is 

 incontrovertible, it results that the fern must now be 

 regarded, not only as ranking amongst the exogenous 

 Cryptogams, but as taking a high position in that well- 

 characterised group. 



Stem or Branch. 

 Transverse. 



N.— p. 289, Fig. 1, C.N. 1302. 





