PRIMARY STRUCTURE OF CERTAIN PALEOZOIC STEMS. 365 



Figs. 14-18. Pitys antiqua. 



Fig. 14. Transverse section, showing part of the pith and secondary wood, a; 2 , v.b. 13, double primary 

 xylem-strand, in contact with the secondary wood ; v.b. 12a, xylem-strand, deep in the pith, perhaps a repara- 

 tory strand. {Of. diagram 5 in text, p. 347.) x 40. (K. 598 c .) 



Fig. 15. Transverse section, v.b., primary xylem-strand, embedded in the pith; px, protoxylem of the 

 strand ; x 1 , part of secondary wood, with broad medullary rays, m.r. The xylem-strand is that numbered 3 

 in diagram 5. (See p. 348.) x about 110. (K. 598\) 



Fig. 16. Tangential section, passing medianly through a primary xylem-strand (numbered v.b. 2 in 

 photograph 7) embedded in the pith, px, protoxylem-elements of the strand ; r.t., a reticulated tracheide ; the 

 meshes of the reticulation are bordered, in reality, as in the element shown in fig. 17. (See p. 348.) x 140. 

 (K. 598 D .) 



Fig. 17. Part of one of the innermost tracheides of the secondary wood, showing transition from 

 reticulations to bordered pits. (See p. 348.) x 200. (K. 598 E .) 



Fig. 18. Radial section through the secondary wood, showing a medullary ray, and tracheides with 

 multiseriate, hexagonal, bordered pits. (See p. 352.) x 120. (K. 598 E .) 



Platb VI. 

 Figs. 19 and 20. Pitys antiqua. 



Fig. 19. Tangential section through the secondary wood, showing tracheides, and medullary rays of 

 various dimensions. The large ray to the right has gaps in its tissue. (See p. 351.) x 32. (K. 598 G .) 



Fig. 20. Tangential section, from inner part of secondary wood, m.r., medullary rays; the larger of 

 the two contains a definite lacuna, g. ; t.p., bordered pits, on the tangential wall of a tracheide. The pits to 

 the right are on radial walls seen obliquely. (See p. 352.) x 200. (K. 598 H .) 



Fig. 21. Pitys Withami. Transverse section, showing a primary xylem-strand, v.b., embedded in the 

 pith. £ 2 , inner part of secondary wood. (See p. 354.) x about 130. From Witham's original section 

 shown in phot. 10. 



Figs. 22 and 23. Pitys primseva. 



Fig. 22. Tangential section of the secondary wood, to show the ordinary form of the medullary rays, 

 large and small. (See p. 355.) x 36. (K. 211.) 



Fig. 23. Tangential section of the secondary wood near the branch (represented in phot. 11), to show 

 the dilated form of the rays, and tortuous course of the tracheides, in this region. (See p. 355.) x 36. 

 (K. 216.) 



Figs. 24 and 25, Darfoxylon Speneeri. 



Fig. 24. Transverse section showing a double primary xylem-strand, v.b., in contact with the secondary 

 wood, a; 2 ; px, one of the protoxylem-groups of the primary strand, p.p., pith. (See p. 358.) x 150. 

 (W. 1381.) 



Fig. 25. Tangential section through the secondary wood, showing the tracheides, t, and the narrow 

 medullary rays, m.r. (See p. 358.) x 120. (W. 1382.) 



