316 



CALAMITES. 



[CH. 



of the pith-cast, and that such external features are connected 

 ■with the arrangement of the tissues in the vascular cylinder. 

 The indication of grooves and ridges on the bark of fossil Ca- 

 lamites is no doubt the result of the existence in the hypoderm 



N.I. 



NJ2. 



N.3. 



Fig. 77. Portion of a Calamite stem, showing the surface of the bark, c ; the 

 wood, 6; the surface of the pith-oast, a. N.l — N.B. Nodes. -R. Boot. 

 (After Grand'Eury. Partially restored from a specimen in the Ecole des 

 Mines, Paris.) | nat. size. 



of firm strands alternating with strands of less resistant cells. 

 It is very common to find Calamite pith-casts covered with 

 a layer of coal presenting a ribbed surface, but this is simply 

 due to the moulding of the coaly film on an internal pith-cast. 



