lOO 



THE CHAIN OF LIFE. 



which does not appear to have become dominant till near the 

 close of the Mesozoic, but which already existed, though 



I) 



Fig. 92.— a Devonian Taxine ConVer {Dadoxylon ounngondianum, Dn.)- St. John^ 



New Brunswick. 



A, Fragment showing Stembergia pith and wood ; a, Medullary sheath ; b, Pith ; 



c. Wood ; d. Section of pith. 



B, Wood cell a, and hexagonal areiile and pore b. ,,,,.„ 



c Longitudinal secti. n of wood, showing n, Aredation, and b. Medullary rays, 

 u', Transverse section showing a. Wood-cells, and b. Limit of layer of growth. 



perhaps only in few species, and only in upland and inland 

 positions, as far back as the Middle Devonian. 



The Devonian flora seems to have been introduced in the 



