STRUCTURE AND AFFINITIES OF A LEPIDODENDROID STEM. 931 



Plate III. 



Fig- 16. Transverse section through the secretory zone sc, the meristem-zone cm., and the edge of the 

 wood ; t' and t", tracheids ; m, rneristem cells surrounding the secondary tissue of a leaf-trace, x 90. 



Fig. 17. From the same region as fig. 16, passing through a fan-shaped group of meristem cells. 

 x90. 



Fig. 18. Transverse section of the phelloderm showing some older secretory canals. x 80. 



Fig. 19. Transverse section of the outer edge of the secondary xylem, t' t", the meristem region, cm, 

 and a leaf -trace with its cambium arc, m. x 100. 



Fig. 20. Tangential section of phelloderm cells with vacuolated cell-contents. x 80. 



Fig. 21. Oblique radial longitudinal section of a leaf -trace, showing the primary and secondary xylem, 

 a, b and c, region close to the secondary xylem. sc, secretory zone. x 100. 



Fig. 22. Radial longitudinal section of phelloderm cells. x 50. 



Fig. 23. Tangential section of a portion of a leaf-trace, m, meristematic cells. x 120. 



Plate IV. 



Fig. 24. Transverse section showing the corona (x) and secondary xylem (x"). x 50. 



Fig. 25. Radial longitudinal section of one of the large innermost tracheids of the primary xylem, with 

 some small isodiametric tracheids in the peripheral region of the pith. x 90. 



Fig. 26. Bordered pits with fine threads in the wall of a tracheid. x 240. 



Fig. 27. A cell from the phelloderm (outer portion) with thickened wall. x 100. 



Fig. 28. Portion of fig. 21, PI. III., more highly magnified. 



Fig. 29. Tangential longitudinal section showing the double bordered pits in the walls of adjacent 

 tracheids, and the single bordered pits between the tracheids and medullary-ray cells. x 240. 



Fig. 30. Tangential longitudinal section of the secondary xylem showing a leaf-trace in a medullary 

 ray. x 50. 



Fig. 31. A secretory group of cells in the phelloderm. x 90. 



Fig. 32. Radial longitudinal section showing a medullary ray traversing the secondary xylem. x 50. 



Fig. 33. Diagram of the annular primary xylem x, with remains of pith. The dots . . mark the 

 position of two indentations in the ring of wood. 



Fig;. 34. Diagrams illustrating the external contour of the corona. 



VOL. XXXIX. PART IV. (NO. 34). 7 D 



