X] 



CALLUS WOOD. 



319 



node. The mottled or watered appearance of the wood is due to 

 numerous medullary rays which sweep across the tracheids.' The 





/■■■■<■■ «N5''=-i'ivv'w4iiMaKi««^ 





Fig. 79. Longitudinal section of the specimen stem in fig. 78. 



From a specimen in the Williamson Collection, British Museum (no. 80). 

 f nat. size. 



periderm elements, as seen in longitudinal section, are fibrous in 

 form. 



The development of cork in a younger Calamite stem is 

 clearly shown in a specimen described by Williamson and Scott 

 in their Memoir of 1894. In a transverse section of the stem 

 several large cells of the inner cortex are seen to be in process 

 of division by tangential walls, and giving rise to radially 

 arranged periderm tissue ^- 



The section diagrammatically sketched in fig. 80 is that of a 

 Calamite twig in which the wood appears to have been injured, 

 and the wound has been almost covered over by the formation 

 of callus wood. The young trees in a Palaeozoic forest might 

 easily be injured by some of the large amphibians, which were 

 the highest representatives of animal life during the Carboni- 

 ferous period, just as our forest trees are often barked by deer, 

 rabbits, and other animals. Fissures might also be formed by 

 the expansion of the bark under the heating influence of the 

 sun's rays^. Such a specimen as that of fig. 80 gives an air of 

 living reality to the petrified fragments of the Coal period trees. 



1 Williamson and Scott (94), p. 888. 



2 Hartig (94), pp. 149, 297, etc. 



