PLATE 3- CORDAITES J>RAM>I.IN'GII. Radial section of the transition zone next 



the pith, showing the protoxylem to be wholly composed of spiral tracheids. 

 X 153-4 



IM.ATK .). CORDAITES BRANDLINGII. Radial section of the transition zone imme- 

 diately external to the preceding, and showing the spirals of the tracheids 

 passing into scahu iforni structure. X 153.4 



