PRIMARY STRUCTURE OF CERTAIN PALEOZOIC STEMS. 363 



EXPLANATION OF PLATES I.-VI. 

 Plates I. and II., Photographs, taken direct from the sections, by Mr L. A. Boodle, F.L.S. 



Plate I. 



Photographs 1 and 2. Calamopitys fascicularis. 



Phot. 1. Transverse section, showing the pith (only preserved in its outer portion) and the surrounding 

 secondary wood. A, B, C, arrows pointing to the principal primary xylem-strands. A, rather small xylem- 

 strand, at the border of the pith; B, large strand (shown in detail in phot. 2) just entering the secondary 

 wood ; C, strand passing out through the wood. (See p. 332.) x about 10. From the Williamson specimen. 

 (W.* 1380.) 



Phot. 2. Transverse section, showing the xylem-strand B, more magnified, with its central protoxylem ; 

 p, part of pith. (See p. 338.) x about 30. (W. 1380.) 



Phots. 3 and 4. Calamopitys beinertiana. 



Phot. 3. General transverse section, showing the large pith, containing several sclerotic nests,, and the 

 surrounding wood. (See p. 342.) x about 2|. (K. 677.) 



Phot. 4. Radial section, showing the pith, p, and part of the wood, x 2 . The pith contains several 

 sclerotic nests. (See p. 342.) x about 4. (K. 677'.) 



Phots. 5-7. Pitys antiqua. 



Phot. 5. General transverse section, showing the large pith, surrounded by secondary wood, l.t., a leaf- 

 trace, passing out through the wood. (See p. 346.) x about 3. (K. 598 A .) 



Phot. 6. General radial section, showing the pith, p, with horizontal gaps in its tissue, and on one side 

 the secondary wood, x 2 . v.h., a primary xylem-strand. (See p. 346.) x 3^. (K. 598 E .) 



Phot. 7. General tangential section, passing through the outer part of the pith, and the inner secondary 

 wood, x 2 . x 2 , wood in oblique section ; x 2 ', portion of wood in tangential section. Six primary xylem- 

 strands, v.b., are shown; v.b.', a double strand in contact with the secondary wood, x 2 '. v.h. 2, the primary 

 strand shown in detail in fig. 16. (See p. 349.) x 4*. (K. 598 D .) 



Plate II. 



Photographs 8 and 9. Pitys antiqua. 



Phot. 8. Transverse section, showing part of pith,/), and secondary wood, x 2 . v.b., v.b., double primary 

 xylem-strand, embedded in the pith, numbered 38 in diagram 5, in the text. (See p. 347.) x 35. (K. 598 c .) 



Phot. 9. Transverse section showing pith, /), and wood, x 2 . v.b. 13 a , and v.b. 14, two primary xylem- 

 strands, indicated by arrows, and numbered as in diagram 5, with isolated tracheides between them. (See 

 pp. 348 and 350.) x 350. (K. 598 c .) 



Phot. 10. Pitys Withami. General transverse section, showing large pith, surrounded by secondary 

 wood, l.t., arrow pointing to outgoing leaf-trace bundle. Note the concentric rings in the secondary wood. 

 (See p. 354.) x about 3. From one of Witham's original sections in the Edinburgh Botanical Collections, 

 marked "Craigleith, 1831," and figured in his Internal Structure of Fossil Vegetables, pi. vi., figs. 5-8. 



Phot. 11. Pitys primxvu. Tangential section through secondary wood, showing base of a branch, br. 

 m.r.', region in which the dilated medullary rays, shown in detail in fig. 23, occur. In other parts the rays 

 show the ordinary structure, as shown in fig. 22. (See p. 355.) x about 4. (K. 216.) 

 Phots. 12 and 13. Dadoxylon Spenceri. 



Phot. 12. General transverse section, showing the obtusely pentagonal pith, and the surrounding wood. 

 l.t., l.t., two double leaf-traces passing out almost horizontally through the wood, v.b., arrow pointing towards 

 the angle of the pith where the double xylem-strand shown in phot. 13 is present. (See p. 358.) x 4|. 

 (S. 1504 — from Spencer Collection.) 



Phot. 13. Transverse section showing secondary wood, and outer border of pith, p. v.b., pair of mesarch 

 primary xylem-strands, in contact with the secondary Wood. (See p. 358.) x about 50. (S. 1504.) 



The letter W. indicates the Williamson Collection, K. Mr Kidston's Collection, and S. that of the author. 

 TRANS. ROY. SOC. EDIN., VOL. XL. PART II. (NO. 17). 3 h 



