70 



transverse section. The figui-ed piece shows the beginning of the 

 formation of the dark bands (a) between the tracheids — possibly 

 occupying the position of the medullary rays. The same specimen 

 shows also that the dark bands in the jet are parallel to the rows 

 of tracheids (this is not seen in the photograph, but is readily 

 recognised on a careful examination of the actual section). The 

 Text-figs. 6 and 7 were drawn from this section. 





r^ 



"i-ii-hSf 



Fig. 6. — Transverse section of coniferous wood passing into jet. Highly 

 magniiied. 51,448. , 



Other specimens: — 51,451. This section and 51,639 were 

 probably cut from the same specimen. The section consists of 

 sUicified coniferous wood containing patches of jet. Annual rings 

 are faintly shown, as in 51,487. The jet shows several folded and 

 contorted dark bands, as in Figs. 5 and 7, the general direction of 

 which is parallel to the rows of tracheids in the unaltered patches 

 of wood. The portions converted into jet afford evidence, in th& 

 zigzag course of the dark bands, of considerable contraction. 



