

220 CONIFERALES [CH. 



pitting in the ray cells, and by the occurrence of numerous pits in 

 the tangential walls of the summer tracheids. 



Pinuxylon is used by Gothan in preference to Pinoxylon, the 

 name adopted by Knowlton 1 for wood in which there are no resin- 

 canals in the medullary rays. In Pinuxylon the walls of the 

 epithelial cells are thin, rarely thick; the medullary rays have 

 large simple pits in the spring- wood ; there are no spiral bands in 

 the tracheids. The horizontal tracheids have smooth or dentate 

 walls and the Abietineous pitting is much reduced. The distinctions 

 on which these two genera are based are thus not very clearly 

 defined and it is only in particularly well-preserved material 

 that the two generic types can be recognised with certainty. 

 Dr Stopes 2 follows Jeffrey and Chrysler 3 in regarding Gothan's 

 twofold division as unnecessary. 



In the majority of species referred to Pityoxylon the published 

 information is insufficient for a sub-division in Gothan's sense and 

 as a rule the generic name stands for wood of an Abietineous type 

 which cannot be assigned with confidence to any one recent genus. 

 The question of the antiquity of the Abietineae has been confused 

 by the too liberal use of the term Pinites by Goeppert and some 

 other authors for stems which have no claim to be placed in the 

 genus Pityoxylon. Jeffrey and Chrysler 4 , who follow previous 

 authors in quoting Pinites Conwentzianus Goepp. 5 , described as a 

 Carboniferous species from Waldenburgh, as evidence of a Palaeo- 

 zoic Pinus-like wood, state that the species receives 'full confir- 

 mation from the description of a similar type, Pityoxylon chasense 

 Pen. 6 from the Permian of Kansas.' Goeppert and Stenzel state 

 that Pinites Conwentzianus was found on a rubbish-heap ('Halde'), 

 but Goeppert apparently entertained no doubt as to its Carboni- 

 ferous age. Through the courtesy of Prof. Freeh of Breslau I was 

 able to examine the original sections and convinced myself that 

 the wood is Abietineous: the rings of growth are well defined: 

 horizontal tracheids occur in some of the rays and the tracheal 

 pits, 1 2 rows, are widely separated, though occasionally the pits 



1 Knowlton in Ward (00) B. p. 420. 2 Stopes (15). 



3 Jeffrey and Chrysler (06). * Ibid. p. 13. 



5 Goeppert and Stenzel (88) p. 54, Pis. XL, xn. 



6 Penhallow (00) p. 76; Thomson and Allin (12). 



