398 SPHENOPHYLLUM. [CH. 



but it evidently bore foliage in which the leaves were deeply 

 divided, as in Sphenophyllum trichomatosiim (fig. 110, B). 



Fig. 106. Sphenophyllum plurifoliatum, Will, and Scott. 



From a photograph by Mr Highly from a section in the Williamson Collec- 

 tion (no. 899). X 27. 



In this species there are no canals at the angles of the 

 primary xylem, and there are fewer spiral tracheae than in 

 S. insigne. The tracheae of the secondary wood have numerous 

 small pits on the radial walls, and the medullary rays are 

 chiefly composed of parenchymatous cells, which appear in 

 transverse section as groups of cells between the truncated 

 angles of the tracheae. The characters are fairly well seen in 

 the xylem portion of a stele shown in fig. 106. The fascicular 

 wood includes some rows of parenchymatous medullary-ray 

 cells in addition to the characteristic groups, as seen in the 

 figure. A slightly oblique transverse section of a stem is often 

 convenient in the interpretation of histological features ; one of 

 the sections of S. plurifoliatum in the Williamson collection 

 (no. 893), which has been cut somewhat obliquely, shows very 

 clearly the differences in pitting exhibited by the different 

 xylem elements. 



