124 l^R- W- C. Williamson on 



conditions indicated a Cryptogamic plant and the second a 

 PJianerogani. The conflicts of opinion to which these two 

 conclusions led have been referred to on a previous page. 

 The essential characteristics of the two groups now became 

 one of internal organisation rather than of external contour. 

 The end of all this has already been explained in the 

 introduction to the Lepidodendra. The Sigillarice are now 

 reunited with the Cryptogams, and the essential distinction 

 between them and the Lepidodendra again becomes one of 

 external contour. The group, as now generally recognised 

 is restricted to the genus Rhytidolepis of Sternberg and 

 Brongniart's genus Favularia — the two representing the 

 Sigillarice verce of that author, combined with the smaller 

 division of the Leioderniarice of Goldenberg. 



From the magnitude of these trees, and their vast 

 numbers, they must have been a conspicuous feature of the 

 Carboniferous forests ; yet it is a remarkable fact that 

 extremely few fragments of them have hitherto been dis- 

 covered in which their internal structure is preserved. 

 Brongniart himself obtained and described one such frag- 

 ment of Sigillaria elegans* and at a later period MM. 

 Renault and Grand Eury described another, Sigillaria 

 spinulosa.\ 



In 1 87 1 I obtained two fragments, one of the iv?t'?//rtr/rt// 

 type and the other a true Rhytidolepis, both of which I 

 figured and described in my Memoir II. They both proved 

 to be portions of the cortex, only one of them extending 

 inwardly beyond the prosenchymatous zone. The cortex of 

 each corresponded exactly with that of the Lepidodendra, 

 and in the Favtilarice, though not well preserved, we see 

 distinct evidence of a medulla enclosed within a primary 

 tracheal cylinder. In no single feature did these sections differ 



•Archives du Museum D'Hist. Nat. Vol. I. (1S39) p. 406. 

 t Memoirs presentes par divers savants a I'Academie des Sciences de I'lnsti- 

 tut National de France, Tome XXI L No. 9. 



