OF LOWER GREEXSAXD PLANTS. 99 



Resin -cells. Elements whose appearance and blackened 

 contents are highly suggestive of resin-tracheids are scattered 

 through the wood. They occur singly in the uniform tracheid- 

 rows, and many of them appear to have walls which are nearly 

 twice as much thickened as the adjacent elements. Apart from 

 that associated with the resin-canals, which has already been 

 mentioned, resin-parenchyma has not been recognised. 



formal resin-canals run vertically and horizontally through- 

 out the wood, as described above (PI. IV, fig. 2, r.c.a., & PL V, 

 fig. 1, >*.e.). They are lined by an epithelium which appears to 

 be thin- walled, no evidence having been found, even after 

 careful examination, of thickened or pitted epithelium. The 

 average diameter of the canals is about 150-170 //,. In some 

 of the canals the lumen is blocked or partly blocked by out- 

 growths of ty loses. 



The prominent uniseriate medullary rays are composed of 

 elements averaging from 24 to 30 /* in tangential diameter. 

 They are distant from 2 to 9 (3 and 5 being the commonest) 

 tracheid-rows ; the preservation being indistinct, the pitting is 

 not apparent in transverse section, but in radial section it 

 is clear that the rays are composed of two kinds of elements 

 (text-figs. 24, 25). The larger darker cells with thick, some- 

 what blackened walls have simple large pits, one for each 

 tracheid-zone (text- fig. 24, c.). Above and below these, and 

 sometimes forming bands in between them (as at tr. 1 , text- 

 fig. 23) are the r&y-tracheidt, which have thickened walls with 

 smaller bordered pits. These are not the most highly specialised 

 form of ray-tracheid, and have fairly regular outlines, but some 

 show a slight degree of bulging and irregularity of the outer 

 wall (as at tr., text-fig. 24). Among living Pines, tracheids of 

 this type are found in Plnus rejlexa, P. wonticola, and others. 

 The figure of the ray in P. reflexa, given by Penhallow (1907 A, 

 p. 84, text-fig. 24), should be compared with the upper part of 

 text- fig. 24 from the fossil. 



In tangential section the distinction between the tracheids 

 and the larger contents-containing parenchyma-cells is clear 

 (text-fig. 24, tr. & c. ; PL V, fig. 1). Rays from 3 to 20 cells 

 high. 



The horizontally running resin canals are seen in the multi- 

 seriate rays, us at r.c., PI. V, tig. 1. 



a 2 



