200 DADOXYLOX. 



appendages -which were borne at equal distances from one another 

 throughout the length of the specimen. Pith solid, parenchymatous, 

 but sometimes the tissues are only imperfectly preserved. The cells 

 are larger in the centre of the pith, and smaller bordering on the 

 wood, where they are 4-5 times higher than broad, and arranged 

 in vertical rows. At the centre, the cells are more irregularly 

 arranged, and are 1-25 times broader than high. Secretory 

 canals, surrounded by a pseudo-sheath of parenchymatous tissue, 

 also occur in this region. They form groups of from 2 to 15 or 20 

 elements. 



Xylem elements exclusively centrifugal, consisting of spiral, 

 annular, and pitted tracheides, as in Cordaites, but the pits are 

 usually less numerous and less crowded, and the central pore is 

 exactly circular and not elliptical. The pits are sometimes uni- 

 seriate, sometimes biseriate, but not pi uri seriate, generally 

 contiguous, rarely distant. The radial rows of tracheides do not 

 form definite bundles, but are grouped together in a variable 

 number of rows, separated by medullary rays. The medullary ray 

 consists of large cells, and is usually only one cell broad, except 

 on the border of the pith. The height of the ray is considerable, 

 and may be as much as fifty superposed cells. The cells are 

 polygonal, elongated in the direction of the ray, generally 5-6 

 times longer than broad. A few oblique small pits occur in the 

 wall of the cells adjacent to the tracheides. Cortex absent. 



Zeiller has figured bacteria found in some of the more altered 

 or decomposed medullary ray cells. He points out that Dadoxylon 

 Pedroi resembles Cordaites in having a large pith. It differs 

 from that genus in the pith being solid and without diaphragms. 

 In the occurrence of secretory canals in the pith, as well as in the 

 size of the pith, this species recalls the structure of the Cycadege. 

 He concludes, however, that this stem has more or less affinity with 

 the Cordaitales, such as perhaps Noeyyerathiopsis and Puryphyllum, 

 but that this suggestion is little more than a conjecture. 



Dadoxylon Pedroi is known only from the valley of the Jaguarao, 

 Brazil. 



Not represented in the British Museum collection. 



