58 DESCRIPTIVE INDEX TO THE PLATES. 



FIG. PLATE PAGE 



13. V. Transverse section of the primary medullary ray, Fig. 12, but made close to the 



cortical surface of the vascular cylinder, b. Vascular rootlet bundle, /. First 

 formed portion of the rootlet bundle,/'. Secondary medullary rays, d. x 30. 

 Cabinet, No. 856 . . . . . . 14, 23 



14. VII. Transverse section of a medium sized vascular cylinder. Medullary cavity, a, con- 



taining an intruded Stigmarian rootlet, g. Vascular wedges, b. Primary 

 medullary rays, V . Obliquely longitudinal sections of rootlet bundles, normally 

 co-extensive with the entire thickness of the cylinder,/! Section of a rootlet 

 bundle escaping from the cylinder,/'. x5 . 14, 17, 23, 24, 25 



15. VIII. Transverse section of a vascular cylinder with its more external cortical layer and 



the bases of three rootlets. Medullary cavity, a. Wedges of the vascular 

 cylinder, b. Outermost cortical parenchyma, d. Meristem zone of bark, d' , 

 Cortical prosenchyma, e. Rootlet bundle,/. Eootlet bundle cylinder,/". Cor- 

 tical zone of rootlet, g. Eootlet cushion, h. X 6^. Cabinet, No. 759 14, IS, 26 



16. V. Transverse section of a young primary medullary ray. Vessels of the xylem cylinder, 



V. Cells of the medullary ray, J. Primary vessels of the rootlet bundle,/'. Later 

 formed vessels,/. Secondary medullary rays, d. x 14. Cabinet, No. 824 14,23,31 

 16a. V. Transverse section of the vascular cylinder of a very youDg Stigmaria. Cabinet, 



No. 773. x 5. . . . . . . .15 



17. IV. Part of a transverse section of a vascular cylinder, including a longitudinal section 



of a secondary medullary ray containing barred Tracheids. Two radial lines of 

 vessels of the cylinder, b, b. Barred Tracheids, b". x 80. Cabinet, No. 767 15 



18. IX. Transverse section of an extremely young root of Stigmaria. Vascular wedges of 



the disturbed vascular cylinder, b. Superficial parenchyma of the cortex, d. 

 Cortical prosenchyma, d'. Eootlets belonging to the root, g, g. x 11. 

 Cabinet, No. 775 . . . . . . 15, 18 



19. IV. Peripheral portion of the transverse section of the vascular cylinder, Fig. 14, PI. VII, 



in which a new zone is being added exogenously. Older vessels of the cylinder, 



b. Imperfectly developed vessels, &c, of the newer zone, b' . x 39 .17 



20. IV. Periphery of a transverse section of a vascular cylinder with an investing cellular 



layer, which appears to be a cambium. Peripheral vessels of the vascular 

 cylinder, b. Procambial cells, c. X 75. Cabinet, No. 744 . 14, 17 



21. X. Transverse section of the bark of Fig. IS, PI. IX. Outer parenchyma, d. Pro- 



senchymatous zone, d'. X 18. Cabinet, No. 775 . . 18, 19 



22. VIII. Outer cortex of a transverse section from the same specimen as Fig. 15, PL VIII. 



Outermost parenchyma, d. Meristem or bark cambium zone, d'. Eadial walls, 

 apparently of the mother-cells of the procambial cells, d'". Prosenchymatous 

 zone, e. X 18. Cabinet, No. 757 . . . . 19, 43 



23. VIII. Transverse sections of the cortex of a much older Stigmarian root than Fig. 22. 



Outermost cortical parenchyma, d. Meristem zone, d! . Cell walls of mother 



cells ? d". Prosenchymatous zone, e. X 18 . . . 19, 21, 43 



24. VIII. Tangential section through the meristem tissue, d' , of Fig. 23. X 9 .20 

 24a. VIII. Tangential section of the tissue, e, of Fig. 23. x 9 . . 20, 21 



25. IV. Transverse section of a fragment of Stigmaria with a considerable development of 



the prosenchymatous zone, e, of Figs. 22 and 23. X 3. Cabinet, No. 795 . 20 



26. VII. A portion of Fig. 25 further enlarged. External pressure has disturbed the 



transversely intersected prosenchymatous cells along the lines e', <?'. X IS .20 



27. XIII. A dichotomous rootlet of Stigmaria . . . . 32, 33 



