290 PITYEAE [CH. 



Archaeopitys. Scott and Jeffrey. 



Archaeopitys Eastmanii Scott and Jeffrey. The genus Archaeo- 

 pitys 1 has recently been instituted for a specimen of a stem from 

 the Lower Carboniferous rocks of Kentucky which differs from 

 Pitys antiqua, the type with which it is most closely allied, in 

 the position and behaviour of the primary vascular strands in 

 the pith. The type-specimen is a piece of stem 2-7 cm. in diameter 

 including a solid parenchymatous pith 5-5 mm. broad and a cylinder 

 of secondary wood. The wood is similar to that of Cordaites; 

 the tracheids have 2 3 rows of pits but for the most part the 

 details of structure are not preserved; the medullary rays are 

 both uniseriate and multiseriate and not very deep ; the structure 

 is more Cordaitean than Cycadean. A characteristic feature is 

 the occurrence of about 30 vascular bundles in the medullary 

 region: these mesarch strands, with the protoxylem near the 

 centre, are scattered through the pith and several lie on the outer 

 edge in contact with the secondary xylem or are partially embedded 

 in the xylem-cylinder. The examination of a series of sections 

 demonstrated the fusion of perimedullary with medullary strands 

 and the occasional union of the strands of both regions with one 

 another. It appears that the perimedullary strands are the leaf- 

 traces while the strands deeper in the pith are merely branches 

 from the peripheral leaf-trace strands. 



In Pitys antiqua the medullary xylem strands are confined to 

 the outer zone of the pith and constitute the leaf-traces: in 

 Archaeopitys, on the other hand, the medullary strands are scat- 

 tered through the pith and the leaf-traces are restricted to the 

 circummedullary region in actual contact with the secondary 

 xylem. In the Devonian genus Callixylon there are similar 

 strands but they are confined to the edge of the pith and are 

 usually in contact with the wood as are the circummedullary 

 strands in Archaeopitys. The grouping of the secondary xylem 

 of Callixylon into wedge-shaped masses at the inner edge of the 

 cylinder is a characteristic feature; this feature is less definite 

 in Archaeopitys and absent from Pitys. 



1 Scott and Jeffrey (14) p. 345, PL xxxi. figs. 3136; text-figs. 4, 5. 



