THE ANATOMY AND AFFINITY OF PLATYZOMA MICROPHYLLUM. 655 



is a simple midrib, and no vascular supply is seen in the small terminal pinnae. At the base of the rachis 

 is a small aborted branch devoid of pinnae. ( x 6.) 



Fig. 10. Transverse section of the stele of Platyzoma. The sclerenchymatous pith is breaking from the 

 stelar ring along the inner endodermis. In this section the difference in thickness between the upper and 

 lower sides of the xylem-cylinder are not so pronounced as in figs. 1, 4, 13, and 63. ( x 36.) 



Fig. 11. An incomplete "reduction" leaf, § inch long. Only a few terminally aggregated reduced 

 pinna) are developed. ( x 6.) 



Fig. 12. A "reduction" leaf, \ inch long, taken from the side of the rhizome. Towards its hooked tip 

 are two small pinnae with simple unbranched veins. ( x 6.) 



Fig. 13. Transverse section of the stele of Platyzoma, showing 3 large leaf-traces departing from the 

 upper surface ; a trace of intermediate size being liberated on the upper portion of the right side ; and 

 small traces departing on right and left towards the lower, surface. ( x 36.) 



Plate II. 



Fig. 14. Transverse section at the base of the petiole of a typical pinnate leaf of Platyzoma. ( 15.) 



Fig. 15. Transverse section of the lower part of the rachis of a typical pinnate leaf. ( x 15.) 



Fig. 16. Transverse section of the upper part of the rachis of a typical pinnate leaf. ( x 15.) 



Fig. 17. Transverse section of the terminal part of the rachis of a typical pinnate leaf. ( x 15.) 



Fig. 18. Transverse section of the very base of a typical filiform leaf. ( x 15.) 



Fig. 19. Transverse section of the same leaf at a slightly higher level in the leaf-base and showing the 



establishment of the lateral grooves. ( x 15.) 



Fig. 20. Transverse section of the same leaf-base at a still higher level. The xylem of the leaf-trace 



has widened laterally, the water-storage tissue is established towards the lower surface, and the flanges and 



grooves are fully developed. ( x 15.) 



Fig. 21. Transverse section at the base of the middle zone of a typical filiform leaf. ( x 15.) 



Fig. 22. Transverse section at the base of the middle zone of another typical filiform leaf. ( x 15.) 



The xylem of this leaf is much more massive than in the leaf seen in section in fig. 21. 



Fig. 23. Transverse section of the upper part of the middle zone of a filiform leaf. ( x 15). 



Fig. 24. Transverse section of a similar portion of another filiform leaf. The xylem is here much more 



massive than in fig. 23. ( x 15.) 



Figs. 25, 26. Transverse sections through the bulbous terminal portions of two typical filiform 



leaves. ( x 15.) 



Fig. 27. Transverse section of the petiole of the reduced leaf depicted in fig. 9, and showing the prepara- 

 tion for the splitting of the xylem prior to supplying the two branches of the rachis. ( x 15.) 



Figs. 28-33. An ascending series of transverse sections of the stele in the basal portion of the 



dichotomised pinnate leaf represented in text-figure 8. The series illustrates the chief steps in this 



dichotomy. ( x 15.) 



Plate III. 



Figs. 34-37. An ascending series of transverse sections of the rachial portion of the small leaf repre- 

 sented in fig. 11. The series illustrates the extra-marginal pinna-trace supply, and the massing and 

 strengthening of the xylem towards the tip of the leaf. ( x 15.) 



Fig. 38-40. An ascending series of transverse sections through the pinnate portion of the small leaf 

 shown in fig. 12. It shows the preparation for and liberation of a pinna-trace. ( x 15.) 



Figs. 41-47. A series of sections showing the origin and liberation of a large leaf-trace from the upper 

 surface of the stele. In fig. 47 the trace is as seen in transverse section on its way out through the 

 cortex. ( x 15.) 



Figs. 48-51. A series of sections showing the origin and liberation of a small leaf-trace from the lower 

 surface of the stele. In fig. 51 the trace is as seen in transverse section on its way out through the 

 cortex. ( x 15.) 



TRANS. ROY. SOC. EDIN., VOL. LI, PART III (NO. 20). 96 



