258 GORDON—SPECIMENS OF SILICIFIED Woon. 
the leaf-traces pass through them. In_ transverse 
sections of the stem these plates have a “herring-bone” 
structure. The xylem shows bordered pits (sometimes 
in more than one series) on the radial walls of each 
tracheide. The preservation is very good. 
No. 4. In this specimen the pith is preserved and consists of 
: large thin-walled parenchyma, but here and there are 
dark-stained elements which probably were resin canals. 
The protoxylem elements are ranged round the peri- 
phery of the pith. The xylem has bordered pits on the 
radial walls, but they are rather indefinite, as also are 
the medullary rays. 
No. 5. The pith is small, with peripheral protoxylems. The 
leaf-traces arise from the protoxylems, and fork in the 
wood, passing out in pairs. They are arranged in pairs 
in a quincuncial series on the outside. The alternation 
of active growth and resting periods seems to have 
varied, and so the zones of small xylem elements vary 
in thickness. The xylem elements have bordered pits 
in a single series on their radial walls; the medullary 
rays are only represented by dark lines. 
No. 6. Similar to No. 5, but of greater diameter. 
No. 7. No tissue preserved. 
No. 8. A wedge of wood some distance from the central pith. 
The branch-traces are single and quincuncially arranged. 
Individual cells of the medullary rays are indistinct, but 
the rays are quite obvious and from 2 to 12 cells high. 
No, 9. This is the best-preserved specimen. The xylem consists 
of cells with one row of bordered pits on their radial 
walls only. The medullary rays are well preserved, 
each cell being shewn, and the lad is from 4 to 12 cells 
high. 
No. 10. This stem shows no internal structure. 
No. 11. The specimen is slightly crushed, and so the cells are 
irregular in shape. Nothing definite of the minute cell 
structure can be discerned. 
No, 12, In this stem the cells are much crushed, and the minute 
structure is indeterminable. } 
