DESCRIPTIVE INDEX TO THE PLATES. 61 



FIG. PLATE PAGE 



inner extremities of the primary medullary rays. Nat. size. Hutton Collection. 

 Newcastle Museum . . . . . .35 



G5. XIII. Natural cast of half of the exterior of the vascular cylinder, b, of the same specimen 

 as Fig. 64, showing the peripheral terminations of the primary medullary rays ; 

 mineral matter replacing the entire bark, d. Hutton Collection . . 36 



66. XIII. A second natural cast, like Tig. 65, showing much more strikingly the peripheral 



termination of the primary medullary rays. Nat. size. Hutton Collection . 36 



67. XIII. Transverse section of a Stigmarian root, nat. size, from which all organic elements 



have been removed. The inorganic matrix occupies the medullary cavity, a, the 

 primary medullary rays, b', and replaces the entire bark, d. Medullary rays, V . 

 Areas left vacant by the disappearance of the vascular wedges of the vascular 

 cylinder, b. Hutton Collection . . . . . :>(5 



68. XIV. Fragment of a Stigmarian root split longitudinally. Exterior of medulla, a. Long 



section of the vascular cylinder, b, b. Primary medullary rays passing hori- 

 zontally through the vascular cylinder, b'. Cortex replaced by inorganic matrix, 

 d, d. Author's Cabinet . . . . . .87 



69. XIV. Exterior of the vascular cylinder of a Stigmaria, from Burntisland. Nat. size., 



showing the large peripheral orifices of the primary medullary rays, intermingled 

 with a few rootlet-scars. Author's Cabinet . . . .37 



70. XII. Fragment of the vascular cylinder of a Stigmaria, upon both surfaces of which the 



bases of rootlet-scars have been impressed on the disappearance of all the other 

 cortical tissues. Nat. size. Author's Cabinet . . . .37 



71. XIII. Cast or impression of the surface of part of a dichotomising Stigmarian root, 



exhibiting the casts of what were longitudinal fissures in the exterior of the 

 bark, along with more minute undulating ridges and furrows. Half nat. size. 

 Hutton Collection . . . . . . .37 



72. XII. Cast of the outer surface of a fragment of Stigmarian bark with undulating corru- 



gations. Nat. size. Museum of the Owens College . . .38 



73. XIV. A normal portion of a Stigmarian root deprived of its rootlets. Cavity left by the 



disappearance of the vascular cylinder, b. Nat. size. Author's Collection . 38 



74. XII. Fragment of Stigmarian bark in which the bases of the rootlets are preserved as 



funnel-shaped depressions, within which the outer cortex of the rootlet forms a 

 prominent ridge at g, and the conical apex of the rootlet cushion is seen at the 

 bottom of the funnel, h. Nat. size. Author's collection . . .38 



75. XIV. Cast of the outer surface of a Stigmarian bark which has been in the condition of 



the specimen, fig. 74. Nat. size. Author's Collection . . .38 



76. XII. Diagrammatic section of a Stigmarian rootlet attached to its bark, d', d", illustrating 



Figs. 74 and 75. Inner surface of the parenchymatous layer, d' . Outer 

 surface of the same, d". Small remnant of the outer cortex of the rootlet, 

 g", g," being the point near which the rootlet, g, had been broken off from its basal 

 end. Cylindrical interior of the rootlet, g', corresponding to the funnel- 

 shaped depressions, h, of Fig. 74, and to the central prominences of Fig. 75. 

 Apex of the cone of the rootlet cushion, h, forming the apical depression of 

 each central prominence of Fig. 75. . . . . .39 



77. XIV. External surface of a Stigmarian bark modified by shrinkage or compression. 



Nat. size. Author's Collection . . . . .77 



