AN EXTINCT PLANT OF DOUBTFUL AFFINITY. 435 



sporangia. Isosporous, possibly in some forms hetero- 

 sporous. 1 



Sphenophyllum plurifoliatum. Williamson and Scott, 

 Phil. Trans., vol. clxxxv., p. 920, pis. lxxv., Ixxxiii., 1894. 



Aster op kyllites Sphenopliylloides. Will. Phil. Trans., 

 vol. i., p. 41, pis. i.-iv., 1874. [Type specimens from the 

 Coal- Measures of Oldham in the Williamson Collection, 

 British Museum.] 



Many linear leaves in each whorl ( 1 8 to 24 ?). Surface of 

 young stems marked by three longitudinal grooves. 

 Medullary rays in the form of groups of parenchymals 

 cells in the spaces between the truncated angles of the 

 secondary tracheae ; the groups connected laterally by 

 means of radially elongated cells. Continuous rows of 

 medullary ray cells rare. Deep seated periderm. 



S. insigne. (Williamson). Phil. Trans., vol. clxiv., 

 p. 41, 1874, and Williamson and Scott. Phil. Trans., vol. 

 clxxxv., p. 926, pis. lxxvi., Ixxxiii., lxxxiv., lxxxv., 1894. 



Aster op hyllites insignis. Williamson. Mem and Proc, 

 Manchester Lit. and Phil. Society, vol. iv. [4], p. 13, 1891. 

 [Type specimens from the Carboniferous beds of Burntis- 

 land ; in the Williamson collection, British Museum.] 



Leaves probably not more than six in each whorl. 

 Cortex grooved in young stems. Tracheae of primary 

 xylem smaller in diameter than in .S. plurifoliatium. 



S. plurifoliatum. — Longitudinal canal at each angle of 

 the primary xylem strand ; spiral tracheae more numerous 

 than in the preceding species. Outer cortex of thinner 

 walled cells than in .S*. plurifoliatum. Tracheae of secon- 

 dary xylem with scalariform markings on radial walls. 

 Medullary rays of regular rows, of one to two cells in 

 breadth, extending through the entire thickness of the 

 xylem. Phloem contains wide sieve- tube-like elements. 

 Deep-seated periderm. 



In describing the fructification of Sphenophyllum, Wil- 



1 Kidston, in his definition of Sphenophyllum, speaks of it as hetero- 

 sporous. The heterosporous example described by Renault is, however, 

 extremely doubtful, and as yet we have no actual proof of the heterospory 

 of this genus (see Kidston, p. 58 ; also Williamson and Scott, p. 942). 



