PLATE XIII. 



Fig. 27. — A dichotomous rootlet of Stigmaria. (Pages 32, 33.) 



Fig. 64. — A natural cast of the medullary cavity of a Stigmarian root, the 

 superficial longitudinal ridges of which represent the prolongations of the medulla 

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

 Collection. Newcastle Museum. (Page 35.) 



Fig. 65. — 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. 

 (Page 36.) 



Fig. 66. — A second natural cast, like Fig. 65, showing much more strikingly 

 the peripheral termination of the primary medullary rays. Nat. size. Hutton 

 Collection. (Page 36.) 



Fig. 67. — Transverse section of a Stigmarian root, nat. size, from which all 

 organic elements have been removed. The inorganic matrix occupies the medul- 

 lary cavity, a, the primary medullary rays, b', and replaces the entire bark, d. 

 Medullary rays, b'. Areas left vacant by the disappearance of the vascular wedges 

 of the vascular cylinder, b. Hutton Collection. (Page 36.) 



Fig. 71. — 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. (Page 37.) 



Fig. 78. — A specimen from the Newcastle Museum of the Stigmaria stellata 

 of Goeppert. (Page 40.) 



Fig. 79. — Transverse section of a Stigmarian rootlet in which the rootlet bundle 

 and its rootlet cylinder, /, is united to the inner side of the rootlet-cortex, g, by a 

 cellular lamina, /", running longitudinally through the rootlet. (Page 32.) 



