198 ANATOMY OF THE GYMNOSPERMS 



I. CORDAITALES 



Growth rings rarely well defined. Wood more or less resinous, but devoid 

 of specialized resin cells or resin reservoirs. Medullary rays all of one kind. 

 Bordered pits on the radial walls of the tracheids, hexagonal and multiseriate. 



1. * * CORDAITES, U.NGER. PLATES 12 AND 13 



Transverse. Pith of the Sternbergia type, the cells large, thin-walled, often 

 resinous. Growth rings, when present, obscure, rarely somewhat conspic- 

 uous. Specialized resin cells and canals wholly wanting except in the 

 bark, where they take the form of tubular, branching canals without epi- 

 thelium, extending in the general direction of the stem-axis. Tracheids 

 in regular, radial rows, conspicuously squarish, and often resin bearing. 



Radial. Elements of the protoxylem spiral and scalariform, and often show- 

 ing a graduated transition into tracheids with bordered pits. Tracheids 

 with hexagonal, bordered pits throughout, on their radial walls only, 

 in 1-5 rows. Ray cells usually of one kind only; the upper and lower 

 walls thin and not pitted ; the terminal walls thin, not pitted, generally 

 curved ; the lateral walls with bordered pits. 



Tangential. Medullary rays rather numerous, i -seriate or often 2-seriate in 

 part. 



This genus is wholly extinct and occurs only in Paleozoic strata. For a 

 more detailed account of the thirteen known North American species, 

 see Penhallow, North American Species of Dado.rylon, Trans. R. S. C., 

 VI, iv, 51-97, 1901. 



SYNOPSIS OF SPECIES 



The following synopsis is given provisionally as an aid to identification of 

 the various species, without implying the absolute value of the differential 

 characters. 



I. Growth rings present 



1. C. pennsylvanicum. 



II. Growth rings obscure or obsolete 

 A. Ray elements of two kinds, tracheids and parenchyma 



Bordered pits in 2-3, rarely 4, rows. 



Ray cells (tangential) oval or oblong, often narrow. 



2. C. Clarkei. 



B. Ray elements of one kind only 



Bordered pits in groups of 6-13. 



Pits on the lateral walls of the ray cells 3-6, chiefly 4, per tracheid. 



3. C. Newberryi. 



