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PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
portion of the root bundle, b. Phloem portion of the same (Liber-cells of 
Van Tieghem). c. Inner cortical cylinder. Enlarged 270 diameters. 
Fig. 14. Usual aspect of the transverse section of a matured rootlet of Stigmaria 
ficoides. a. Vascular bundle, c. Inner cortex, d. Outermost cortex. The 
middle bark is wanting. Enlarged 30 diameters. 
Fig. 15. Transverse section of a matured rootlet in which all the tissues are pre¬ 
served. a. Vascular bundle, b. Small cells in the position of the Liber- 
cells of fig. 13. c. Cylinder of inner bark. d. Outermost bark. e. Middle 
bark. Enlarged 55 diameters. 
Fig. 16. Transverse section of a very young rootlet enlarged 80 diameters, a. First 
formed vessels of the vascular bundle, b. Space left vacant by the dis¬ 
appearance of the Phloem, c. Cylinder of inner bark. d. Outermost cells 
of the outer bark. e. Remnant of the middle bark. 
Fig. 17. Transverse section of the inner cortex, c, and the vascular bundle, «, of 
a similar rootlet to fig. 16. Enlarged 270 diameters. 
Fig. 18. Vascular bundle and inner bark-cylinder of a rootlet like fig. 14. Enlarged 
66 diameters. 
Fig. 19. Similar object to fig. 18. Enlarged 140 diameters. 
Fig. 20. Similar section of the centre of a yet larger rootlet, a. First-formed vessels 
accidentally detached from the bark-cylinder c. a. Newest formed centri¬ 
petal ones. 
Medullary rays of Lepidodendron selaginoides. 
Fig. 21. Part of fig. 7. Enlarged 200 diameters. li. Three vascular wedges. 
Jc, Jc. Two medullary rays containing barred cells. 
PLATE 54. 
Fig. 22. Part of a similar section to fig. 7, but taken from the junction of the 
exogenous zone, h, h, with the vasculo-medullary cylinder a, and exhibiting 
barred cells at the medullary extremities of the medullary rays Jc, k. x. Zone 
of small vessels uniting the vasculo-medullary cylinder with the exogenous 
wedges Ji, h. Enlarged 200 diameters. 
Co. lamostachys Bin neyana. 
Fig. 23. Part of a transverse section of a strobilus of Calamostachys Binneyana in the 
plane of a fertile verticil, enlarged 46 diameters. Jc. Outer cortex of the 
axis of the strobilus. u. Sporangia filled with spores, v. Sporangiophores. 
v", v". Narrow points near the margins of the peltate peripheral extremities 
