OF LOWER GREENS A XD PLANTS. 109 



of the cell-lumen. Comparison of these measurements with 

 those of the majority of gymnospermic woods will show that 

 the wood-elements are throughout small in size. In outline the 

 elements are rounded, and fit closely together. In transverse 

 section, owing possibly to the preservation, pitting is not 

 apparent. In longitudinal section a few of the tracheids show 

 small tangential pits. In the radial walls the bordered pits are 

 circular, as large as to fill the diameter of the tracheid-wall, the 

 pores are circular and large. The pits lie in a single row on 

 the tracheid-wall, in many cases close together, others separated 

 by as much as the width of their own diameter. There is no 

 flattening of the border, the outline always being completely 

 circular. Between the pits traces of " Sanio's rims " are often 

 very conspicuous (text-fig. 27). There are no additional 

 thickening spirals on the tracheid-walls. 



Large areas of wood-parenchyma like those described for 

 Pltyoxyloti Sewardi are not present, nor have I been able to 

 detect any wood-parenchyma cells other than those containing 

 resin (see below). 



Specialised resin-containing tracJieids do not seem to be present. 

 Itesin-containing parenchyma-cells can be recognised in transverse 

 section scattered among the tracheids, but are best seen in 

 radial section. These cells are about the same diameter as the 

 adjacent tracheids, their walls are somewhat thickened, and 

 their transverse walls at right angles to the longitudinal walls. 

 The cells are vertically elongated from twice or three times 

 their transverse diameter to very much more than that, and are 

 filled with blackened or brownish remains of their resinous 

 contents. 



Normal resin-canals are scattered throughout the secondary 

 wood, and one canal lies in each of the main primary bundles. 

 The structure is the same in all cases, the epithelium lining the 

 canals being thick-watted. The pitting on these thick-walled 

 cells is well seen in longitudinal section, where the wall is 

 perforated by a large number of small pits (PL VII, fig. 2, e., 

 & text-fig. 26, e.). In many cases these cells have brownish 

 or fine black granular contents. 



The majority of the canals contain tyloses. These are seen in 

 the primary canals in PL VII, fig. 1, and also in the canals in 

 the secondary wood in PI. VI T, fig. 2, t. A longitudinal view 



