176 



MEGALOXYLEAE 



[CH. 



cases -4 mm. and their iso-diametric or even horizontally 

 elongated and flattened form. Some of these large metaxylem 

 elements are seen in longitudinal section at m in fig. 448 where 

 the shrinkage and partial decay of the parenchymatous tissue 

 have resulted in the separation of transverse bands of xylem 



A B 



It 





FIG. 446. Megaloxylon Scotti. A, B. Transverse and longitudinal sections, 

 a; 1 , x 2 , primary and secondary xylem ; It, leaf-traces. Nat. size. C. Secondary 

 xylem. 



simulating the discoid pith of a Cordaites. The walls of these 

 tracheal cells are covered with multiseriate pits. With the 

 short and sometimes flattened xylem elements occur others of 

 greater length, but these are chiefly met with in the more peri- 

 pheral part of the central region where some of the tracheids are 



